The causes of the Second World War are neither singular or straightforward. This section will explore the primary causes which led to the outbreak of war in 1939.

Germany’s foreign policy

Germany’s aggressive foreign policy was not the sole cause of the Second World War, but it was a large contributing factor.

From 1935 onwards, Germany had actively pursued an aggressive foreign policy: reintroducing conscription, creating the Luftwaffe, planning for war as detailed in the Hossbach Memorandum of 1937, and occupying Austria, the Sudetenland, and Czechoslovakia before eventually invading Poland in 1939.

By breaking international agreements set out in the Treaty of Versailles and pursuing aggressive expansionism, Germany’s actions made a major European war more likely.

The aftermath of the First World War

Following the end of the First World War, the Treaty of Versailles was agreed. Whilst a temporary economic recovery appeared between 1924-1929, Germany remained politically and economically fragile.

The Wall Street Crash in 1929 once again decimated the economy, and the resulting economic instability created political instability. The political instability from 1929-1933 led to disillusionment with politics and a rise in support for extremist parties such as the Nazis.

The Treaty of Versailles also reduced the size of Germany. This had numerous outcomes, among them losing key economic outputs, as well as making people who had previously been German part of other countries. The change in the eastern borders of Germany in particular became a source of contention, and as a result many people within Germany felt that the treaty was unfair. This again led to discontent and was exploited by extremist parties such as the Nazis who rejected of the treaty.

Weakness of the International System and the Policy of Appeasement

Whilst Germany’s foreign policy played a decisive role in the outbreak of the Second World War, the failure of other countries to react, or their inability to react, was also key.

The aftermath of the First World War had also left France and Britain in politically and economically weak situations. This meant that they were often unwilling or unable to respond effectively to German aggression.

Britain in particular felt that the Treaty of Versailles, and its effects on Germany, were harsh. Following the devastation of the First World War, Britain was desperate to avoid another world war. As a result of this followed a policy of appeasement towards Hitler’s aggressive foreign policy from 1933-1939. This policy boosted Hitler’s confidence and as a result his actions became progressively more bold.

Outside of mainland Europe, the USA and the Soviet Union also played key roles in the outbreak of the Second World War. In the lead up to 1939, both countries followed increasingly isolationist policies, keeping themselves out of international foreign affairs where possible.

The USA had not joined the League of Nations, and had passed several Neutrality Acts in 1938 which avoided financial and political war-related deals.

As a major power, the USA’s reluctance to involve itself in other countries affairs helped to embolden Hitler and the Nazis. This contributed to the rise of Nazism in Europe, and its confidence to carry out its aggressive foreign policy without fear of retaliation from the USA.

In addition to this, following the Nazi-Soviet Pact of 1939 , the Soviets ceased to be an immediate threat to the Nazis. This allowed them to start the war for Lebensraum with Soviet support.

When combined, these factors reduced the chances of an effective challenge to Nazi Germany preceding the Second World War. It meant that Hitler was able to get progressively more confident without fear of retaliation or serious action from other powers.

Creation of the Axis Powers

Throughout the 1930s, new alliances were forged across Europe.

The Spanish Civil War (1936-1939) helped to unite Italy and Germany, who both offered military support to the nationalist rebels attacking the democratic government.  Prior to this, Italy and Germany had not been militarily aligned, and Italy had blocked Germany’s plans to annex Austria in 1934.

Following the Spanish Civil War however, relations between the two countries improved. In October 1936, the Rome-Berlin Treaty between Italy and Germany was signed.

The following month in November 1936, an anti-communist treaty, the Anti-Comintern Pact, was signed between Japan and Germany. In 1937, Italy joined this pact.

The three countries formalised these pacts into a military alliance in 1940. The countries that were part of this alliance became known as the Axis Powers. When coupled with Germany’s aggressive foreign policy, the creation of an alternative military alliance to the Allies, intensified the volatile situation.

The failure of the Allied Powers in summer 1939

The Soviet Union and Nazi Germany were ideological enemies. Despite this, the Soviet Union and Nazi Germany entered into a non-aggression pact in the summer of 1939, which allowed them to invade and occupy parts of Poland. This pact suited both countries territorial aims.

This situation however, was not inevitable. In 1939, the Soviet Union was initially engaged in talks with the Allies over a defensive strategy for Poland. When these talks broke down, the Soviet Union turned back towards Germany, quickly agreeing the Molotov-Ribbentrop Pact.

Ultimately, the Allies failed to make a concerted effort to work together to prevent Hitler’s attack on Poland. This failure was a contributing factor in the outbreak of the Second World War.

The Nazis invaded Poland on 1 September 1939.

The Nazis justified the invasion by suggesting that Poland had been planning to invade Germany, and with false reports that Poles were persecuting ethnic Germans.

On 17 September, the Soviet Union joined forces with Germany and invaded Poland.

The Nazis and Soviets used an encirclement tactic to occupy Poland, sending troops in from all directions. Over 2000 tanks and 1000 planes were used to advance on Warsaw, the Polish capital. By the 27 September 1939, just 26 days after invasion, Poland surrendered to the Nazis.

Following the surrender, the Nazis and the Soviets divided Poland between them, as had been secretly agreed in the Molotov-Ribbentrop Pact.

The western area of Poland was annexed into the Greater German Reich. The Soviet Union took the eastern section. On 23 October 1939, the area not annexed to Germany or the Soviet Union was placed under the control of a German administration led by

. This administration was called the

.

The period of war following the invasion of Poland is often referred to as The Phoney War. This is because between the Allied declaration of war and the German invasion of France and the Low Countries there was little real action, with just one small land operation (when the French invaded Germany’s Saar district) in the whole of western Europe.

After the occupations of Denmark and Norway in April and early May 1940, Hitler invaded France on the 10 May 1940.

As a German attack on the French-German border was unlikely due to the

of defences, the Allies (Britain, France, Belgium, Luxembourg and the Netherlands) had expected and prepared for the Nazis to follow the same line of attack as in the First World War, through Belgium. Thus, the Allies concentrated their troops near the Franco-Belgium border.

The Germans, however, split their attack into three fronts, A, B and C.

Group B were tasked with invading and defeating The Netherlands as quickly as possible, and then engaging the Allies in combat in central Belgium.

Group C were tasked with invading the Maginot Line of defences, engaging the French troops defending this line and distracting them from Group A.

Group A were the main focus of the German offensive. They were tasked with going through the middle of Group B and Group C, through the dense Ardenne Forest in south-east Belgium and Northern Luxembourg.

From here, they advanced straight to the coast, which they reached on the 20 May 1940. Here, they captured key ports whilst also encircling a huge number of French and British troops in Northern France and Belgium, who had been fighting Group B of the German attack.

The Allied troops were divided. Over 300,000 of the Allies’ strongest troops encircled in Northern France and Belgium retreated to England in

between 26 May 1940 and 4 June 1940.

On 29 May, Belgium surrendered. The German Army pushed on towards Paris, capturing the city on 14 June 1940.

After just six short weeks, France surrendered to the Nazis on 25 June 1940.

Less than a year after invading Poland, Germany had occupied, or become allied with, a large part of Europe.

Following the invasion and subsequent occupation of France, the Nazis turned their attention towards Britain.

The Nazis assumed that, due to the defeat of almost all of their allies, Britain would be willing to agree to a negotiated peace deal.

The British government, however, doubted that Germany’s true aims were to maintain peace, and were unwilling to consider a peace deal.

In the face of this opposition, the Nazis began to step up planning for Operation Sealion – the code name for the invasion of Britain. The first challenge for the Nazis was to destroy the British Royal Air Force (more commonly known as the RAF). As a result, the Battle of Britain was an air battle between the Luftwaffe, the German Air Force, and the RAF.

The Luftwaffe initiated the first attack as part of the Battle of Britain on 10 July 1940. For the first six weeks the Luftwaffe concentrated on bombing strategic targets, such as air strips, on the south coast. After a series of battles, it became clear that the Nazis were not going to enjoy a swift and easy victory.

In mid-August the Nazis switched tactics and deployed the Luftwaffe to bomb RAF runways and airports.

A key turning point in the battle was the bombing raid on London’s East End on 24 August 1940, and the subsequent bombing of Berlin on 25 August 1940. Göring, who had ordered the initial attack, persuaded Hitler to retaliate and order a mass bombing of London. This decision marked an active switch to bombing civilian targets.

Whilst devastating for London, the bombing raids on the East End allowed the RAF crucial time to recover from the raids on their own runways and airports.

On 14 September 1940, Hitler recognised that invading Britain was, at that moment, impossible. Operation Sealion was postponed indefinitely. The bombing of London, which became known as the Blitz, continued until 11 May 1941.

On the 10 June 1940, Italy, Germany’s main European ally, declared war in North Africa, hoping to make territorial gains.

The British, who had troops stationed in Egypt (which was a colony at the time), responded four days later by capturing the Italian Fort Capuzzo in Egypt.

A series of counter offensives followed. The Italians soon captured Sidi Barranim, a town near the border of Libya, in September, and the British defeated the Italian Army and the German Afrika Korps in December.

The situation reached a head in the Second Battle of El Alamein in October 1942, which became a key turning point in the war.

The First Battle of El Alamein had stopped the German and Italian troops advance completely in July 1942.

The German and Italian troops were expecting an attack, and sheltered behind a minefield. The Allied invasion took place in two parts: an intense bombing campaign followed by infantry attack which then cleared the way for armoured divisions to break through the German defences.

The German and Italian troops were in a weak position, with their leader, Erwin Rommel, in hospital from 23 September onwards. They also had little fuel or transport. As the Allied troops attacked on 23 October 1942, von Stumme, Rommel’s replacement, had a heart attack and died. Rommel returned from hospital to retake command on the 25 October 1942.

By 2 November 1942, the defences were near breaking point. Rommel withdrew his troops on 4 November 1942. By 11 November, the battle was over, leaving the Allied troops victorious.

The battle marked a turning point in the North Africa campaign, reviving the morale of the Allied troops following the failure of the Battle of France. Following the battle, the Allied troops launched the Tunisia Campaign, the last Axis stronghold in North Africa.

After a winter stalemate in 1942, with both sides building up reinforcements, the Allied troops advanced and surrounded the Axis troops.  On 13 May 1943, the Axis forces in North Africa surrendered. All Axis territory was captured along with 275,000 experienced troops. It represented a significant reduction of Axis power.

The Allies turned their forces to the war in mainland Europe.

Following the failure of the Battle of Britain, the Nazis turned their focus towards their ideological enemy, the Soviet Union. Hitler had always envisioned that a successful war against the Soviet Union would be necessary to achieve two of the Nazis ideological aims: Lebensraum  and the destruction of communism .

Hitler had anticipated the attack being similar, if not easier, than that of France, lasting four or five months at most. The Nazis viewed the Russian people as racially and ideologically inferior: no match for the German army.

Hitler authorised preparations for the attack, known as Operation Barbarossa , on the 18 December 1940.

The Nazis invaded the Soviet Union on 22 June 1941. This broke the Nazi-Soviet aggression pact which had been signed just two years prior. The Nazis aimed their attacks at three key targets, the Ukraine in the south, Moscow in the middle, and Leningrad in the north.

The invasion took the Soviets by surprise. Initially, the Nazis managed to cover large territories and encircle masses of troops, who duly surrendered. By late September, the Nazis were on the edge of Leningrad, having covered hundreds of miles of Soviet territory.

Despite these tactical achievements, Soviet resistance hardened and the country did not surrender. Although less well trained than their German counterparts, the Soviet Army was extremely large and they were more used to the difficult terrain than German troops.

Having expected a quick victory, the German troops became more and more exhausted and they were unprepared for a Russian winter after months of warfare. Supply chains were slow, leaving troops short of key materials.

In late 1941, the Soviets launched a counterattack on the German troops outside Moscow, pushing the Germans back into a defensive battle.

Until the end of 1941, the United States of America had remained a neutral country, not involved in the War.

The Japanese attack on Pearl Harbour, the most important naval base in America, on 7 December 1941 changed this.

The USA were caught by surprise by the attack. Over 2400 people were killed, and more than 1200 people were injured. A large majority of the military vehicles present were destroyed or broken.

The reaction to the sheer devastation caused was immediate. The following day, the United States entered the Second World War, declaring war on Japan.

Hitler supported the Japanese attack, and shortly after, on 11 December 1941, declared war on the USA. The USA immediately retaliated, and returned the declaration.

The bombing of Pearl Harbour, which brought the United States into the war on the side of the Allies, had a huge impact on the final outcome of the war.

Following the invasion of the Soviet Union in 1941, fighting on the eastern front was continuous. The Germans, who had been close to capturing the capital of Moscow in late 1941, were pushed back over 150 miles to west to the town of Rzhev.

This attack was problematic for German morale but, by February 1942, German troops had reorganised. They counterattacked and destroyed several Soviet divisions.

This counterattack was soon met with further counterattacks from the Soviets and then the Germans.

On the 23 August 1942, the Germans launched an offensive to seize the city of Stalingrad in south-west Russia. The battle was one of the largest and most brutal in history. It was also one of the only battles of the Second World War to feature hand-to-hand combat.

The Germans first attempted to bomb Stalingrad into submission. The city was reduced to rubble with air attacks by the Luftwaffe. German tanks followed the planes, reaching the outskirts of the city quickly.

The German troops entered Stalingrad on the 12 September 1942, advanced quickly and occupied two thirds of the city by the 30 September.  Their rapid advance once again fooled them into thinking that the battle would be quick.

The Soviets put up a strong resistance. Having experienced losses against the Germans almost continuously for the previous year, the Soviet Army saw Stalingrad as an ideological and moral battle as well as a tactical one.

In addition to continuous air bombing, fighting in the rubble of the city was characterised by hand-to-hand combat with daggers and bayonets, as each side ambushed the other under the cover of darkness.

With huge losses, both sides ordered reinforcements.

By November 1942, Marshal Georgy Zhukov , the Soviet general, had gathered over a million men with several tank armies. Zhukov encircled Axis troops in the north-west of the city.

On 19 November 1942, the Russians overwhelmed Romanian armies who were supporting the Germans in the north west of the city. The Germans reacted slowly, and quickly became encircled. Despite General Paulus repeatedly requesting permission to surrender or retreat from Hitler, this was denied.

The 100,000 German soldiers that were surrounded by the Soviet Army quickly ran out of ammunition and food in the midst of the Russian winter. Against Hitler’s direct orders, General Paulus surrendered with his remaining 91,000 men on 31 January 1943.

The battle finished on 2 February 1943.

Of the 91,000 German troops that surrendered, just 6000 eventually returned to Germany. Most died from illness, starvation or exhaustion.

The Battle of Monte Cassino took place from 17 January 1944 to 18 May 1944. It was a series of four offensives carried out by Allied troops in central Italy (who was a key ally of Germany) in an attempt to breakthrough the Winter Line and occupy Rome.

Monte Cassino was the mountain above the town of Cassino where the Germans had installed several defences in preparation for the Allied invasion. An Abbey sat on top of the mountain.

One of the primary routes to Rome ran through the town of Cassino at the bottom of the mountain. Other routes to Rome had become impassable due to flooding and the difficult terrain (made worse by the winter weather). However, due to the German defences above, passing along the Monte Cassino route was impossible without first defeating the German troops on the mountain.

Allied troops landed in southern Italy in September 1943, but only had limited progress due to the harsh winter and Axis defences.

The first attack at Monte Cassino started on 17 January 1944 as British Empire, American and French troops fought uphill against the strategic German defences. The German defences were extremely well integrated into the mountainside, and, following large losses, the Allies pulled back on 11 February.

The Allies suspected that the Germans were using the Abbey (which was situated at the top of a large hill and protected as neutral territory under the Concordat of 1933) as a military observation point. In response, the Allies bombed the Abbey, starting the second offensive of the battle, on 15 February 1944.

250 women, men and children were killed in the bombing.  Following the bombing, German troops used the ruins of the Abbey as a fortress and observation post.

The third attack was launched from the north on 15 March. After a large bombing campaign, Allied troops advanced through the town of Cassino. The defences were tough and both sides experienced heavy losses. The German parachute divisions held on to the Abbey.

The Allies fell back, and planned Operation Diadem – the fourth and final battle. The battle involved attacks on four fronts, and took two months to get all the troops in place.

The attack started on the evening of 11 May 1944. By 17 May, the Polish corps broke through the German defences. On 18 May,  Polish troops captured the Abbey at the top of Monte Cassino.

The Battle for Monte Cassino was over, and the Allies had broken the Winter Line. On 4 June 1944, the Allies captured Rome, the capital of Italy.

Despite this success, the Battle had come at a cost. There were over 55,000 casualties for the Allied troops in comparison to 20,000 German casualties.

By the summer of 1944, the Allies had enough coordinated strength to consider an invasion of France. This invasion became known as D-Day.

On the evening of 5 June 1944, under the cover of nightfall, British, French, American and Canadian troops started to cross the English Channel, landing in Normandy. These troops were supported by paratroopers who were dropped behind enemy lines. The next morning, on 6 June 1944, the attack began.

With a huge concentration of troops defending the eastern front in the Soviet Union and the decoy measures implemented, resistance from the Germans was initially weaker than expected. Despite this, the Allied troops experienced over 10,000 losses on the first day.

Despite these losses, the Allied troops made small but significant progress. By 7 June 1944, the Allies had managed to capture the naval port of Cherbourg.

This acquisition allowed Allied troops to flood in to France, fighting their way slowly across France, pushing back the German troops. The Germans had, by this point, received reinforcements, but they were overwhelmed by the sheer number of Allied troops.

At the same time, to coincide with D-Day, the Soviet Union launched an attack codenamed Operation Bagration in Soviet Byelorussia. Fought between 22 June and 19 August, the attack resulted in huge casualties for German troops and destroyed their front line on the Eastern Front. This pushed the remaining German troops back into Poland.

The Germans were now fighting a war on both the Eastern Front, against the Soviet Union, and the Western Front, against Britain, France, and the United States. They were being defeated and pushed back towards Germany, slowly, by both fronts.

Following D-Day and the Invasion of Normandy, the Germans were fighting a defensive war on two fronts.

At this stage in the war, the Germans did not have the resources to sustain this. They were quickly pushed back in France, and retreated into Germany. By March 1945, the Allied troops had crossed the River Rhine.

On the Eastern Front, following the Battle of Stalingrad in 1942 and 1943, the German Army had been pushed into retreat.

By 17 January 1945, Soviet troops had liberated Warsaw, the capital of Poland. On 27 January 1945 the Soviets liberated the Auschwitz Camp complex, which included Auschwitz-Birkenau, the largest Nazi extermination camp.

Both sides of the Allied forces soon entered Germany.

On 16 April 1945, the Soviet troops started the offensive to capture Berlin, the German capital. This offensive started the Battle of Berlin, one of the last huge battles of the Second World War.

Led by Marshal Zhukov, who had successfully commanded the Battle of Stalingrad, Soviet troops encircled Berlin, and started their advance inward. On 30 April 1945, Hitler took his own life in his bunker underneath the Reich chancellery.

On 2 May, Berlin was surrendered to the Allies. On 7 May 1945, the German army commanders surrendered all forces to the Allies.

This surrender ended the war in Europe. However, the World War was not yet over, and continued in Pacific against the Japanese. On 6 and 9 August 1945, two atomic bombs were dropped over the Japanese cities of Hiroshima and Nagasaki, instantly killing over 200,000 people.

On 15 August 1945, the Japanese surrendered.

The Second World War was over.

Germany’s loss of the Second World War was the result of a combination of factors, both in German weaknesses and in Allied and Soviet strengths.

German weaknesses

Germany had four key fatal weaknesses in the Second World War. These were: the lack of productivity of its war economy, the weak supply lines, the start of a war on two fronts, and the lack of strong leadership.

Following the invasion of the Soviet Union, using the Blitzkrieg tactic, the German Army marched far into Russia. However, they did so on very slow, overextended, supply lines.  These supply lines hindered the German advance, and eventually led to a huge lack of supplies on the front line. This, alongside key Soviet advances, contributed to the German retreat.

In addition to the poor supply lines, Germany’s war economy could not support the extent of goods needed for the various invasions in the Second World War. As Richard Evans writes, in Germany ‘by 1944, 75 percent of GDP was being devoted to the war in comparison to 60 percent in the Soviet Union and 55 percent in Britain’ [Richard Evans, The Third Reich at War, (England: Penguin Group, 2008), p333]. Throughout the war, Germany became desperately short of fuel, coal and food.

It was not until Albert Speer became Minister of Armaments and War Production in 1942 that Germany  started moving towards a total mobilisation of the economy for war, although this was still with mixed success. In mid-1944, the economy peaked. For Nazi Germany, in retreat with a defensive war being fought on two fronts, this was too late.

Following the Allies D-Day offensive and the simultaneous Soviet offensive Operation Bagration, Germany was fighting a defensive war on the eastern front and on the western front. This meant that the German troops were split, and neither side could have the full weight of the army. As a result of this, the German troops were pushed back into Germany.

In addition to the above, in the closing stages of the war there was a lack of strong leadership in Nazi Germany. Hitler had lost the faith of the German people, he was rarely seen in public and stayed confined to his bunker under the Reich chancellery in Berlin.

On the 30 April 1945, Hitler took his own life. For many, who had seen Nazism and Hitler as one being, the death of Hitler meant the end of Nazi Germany.

Soviet Strengths

Whilst initially the German invasion of the Soviet Union covered a vast area very quickly, the Soviets soon responded. The German presumption that the Soviets were ‘racially’ and economically inferior and the war in the east would be quick soon collapsed.

The Soviet Union had an enormous amount of manpower to call upon, and despite facing the German troops who were both more experienced and more highly trained, there was a constant ready supply of men to face them. The Soviets also heavily mobilised their women to work in almost all areas for the war effort.

In addition to this, as the war continued, the troops in the Soviet Union became better trained and better equipped for combat thanks to the mobilisation of the Soviet Union’s war economy and the Lend-Lease programme.

Allied Strengths

In the beginning of the Second World War, the Allies were forced into retreat due to early German victories, such as the Battle of France.

The American Lend-Lease programme strengthened the Allies. The Lend-Lease programme was an American policy of giving aid in various forms to the Allies prior to and following the American entry into the Second World War. The Lend-Lease programme started in 1938, but was greatly expanded in March 1941.

In total, under the lendlease programme Britain received thirty-one billion dollars of aid, and the Soviet Union received eleven billion dollars. This aid came in the form aircraft, weapons, ammunition and medical supplies.

Following the American entry into the war, the Allies also had a huge injection of fresh manpower. This undoubtedly aided their success during the D-Day invasions.