What events in the 1930s led to World War II in Europe?

The origins of World War II (1939–1945) in Europe can be traced back to the end of World War I (1914–1918). After the armistice of 1918, Germany was forced to sign the Versailles Treaty. Germany had to pay reparations to the Allies. Germany lost a great deal of territory and had to limit the size of its military. Also, it had to accept blame for beginning WWI. This treaty destabilized postwar Germany and helped pave the way for the rise of Adolph Hitler.

Hitler became chancellor in 1933 and gradually became a dictator. He ignored the Versailles Treaty by rearming Germany; violated the Treaty of Versailles by sending troops into the Rhineland in 1936; helped Francisco Franco win the Spanish Civil War (1936–1939); and seized Austria, the Sudetenland, and the rest of Czechoslovakia.

The British and French failed to stop Hitler's aggressive moves in the 1930s. Instead, they followed the policy of appeasement: they gave in to Hitler's demands in an effort to avoid another world war. America followed a policy of isolationism during the 1930s as it faced the Great Depression, so it played no role in Europe. In 1939, the Soviet Union signed a non-aggression pact with Germany. This enabled Germany to invade Poland in September 1939. Finally, Britain and France declared war against Hitler, and WWII began.

Hitler had long made it clear that he wanted to create a German Empire in Europe. The Western powers, however, were reluctant to confront him militarily, fearing that they weren't sufficiently prepared to engage in armed conflict. So they sought to appease the Nazi regime, trying to accommodate Hitler's territorial designs within a formal diplomatic structure. The policy of appeasement reached its apogee, or nadir, at the notorious Munich Conference of 1938, in which the Western powers allowed Hitler to take over the Sudetenland, a majority German-speaking enclave of Czechoslovakia. Despite his ostensible victory at Munich, Hitler was disappointed with the outcome, believing that he'd been deprived of the additional territory that he sought as part of his imperialist vision.

Hitler, then, had no intention whatsoever of abiding by the agreements he'd made at Munich. It was inevitable, then, that he would seek to conquer more territory by force of arms, which he then proceeded to do by the invasion of Poland in September 1939. The policy of appeasement lay in ruins as the Western powers now realized that Hitler simply couldn't be trusted. In invading Poland, Hitler had crossed the Rubicon and there was to be no going back.

The primary events which led to the outbreak of World War II in Europe were German aggressive expansionary policies in Eastern Europe, primarily the invasion of Poland, which triggered the outbreak. A secondary cause was the reluctance of other European powers to stop German aggression before it erupted into a full blown war.

German Chancellor Adolf Hitler frequently railed against the perceived unfairness of the Treaty of Versailles of 1919, and withdrew Germany from the League of Nations in protest. He later sent German troops into the Rhineland which was occupied by France. Although the French had every right to stop him at that point, they failed to do so. Later, Hitler forced a reunion (anchluss) with Austria claiming he had been invited by the Austrian government to do so. When Hitler demanded the Sudetenland, the German-speaking portion of Czechoslovakia, British Prime Minister Neville Chamberlain flew to Munich and met with Hitler. It was agreed that Hitler to retake the Sudetenland for Germany in exchange for Hitler's promise that he would make no more territorial claims. The Czechs were not allowed to participate in the meeting.

The vacillations of Chamberlain and others convinced Hitler that France and Germany were weak and indecisive; and he next made demands on Poland, ostensibly to protect the interests of German speaking people living in the Polish corridor. At this point, Britain and France more decisively warned him not to proceed against Poland. Rather than heed the warnings, Hitler signed a non-aggression pact with the Soviet Union which contained a secret proviso for the division of Poland between the two powers. Hitler at this point, ready to proceed against Poland and unconcerned about a war, told his generals

My only fear is that at the last moment, some dirty dog will come up with a mediation plan

The German invasion of Poland, Operation Yellow, commenced on September 1, 1939. Two days later, France and Britain issued ultimatums to the Germans to withdraw immediately from Poland. The ultimatums were ignored, and war was declared.  

What events set the stage for World War II in Europe?

There were several events that led to the outbreak of World War II. One event was the Versailles Treaty, which was very harsh on Germany. Germany had to pay the Allies $33 billion in reparations. They also had to accept the responsibility for World War I. Germany resented these harsh actions, and when Germany struggled economically in the 1920s, Adolf Hitler vowed to get revenge.

Other events that led to the start of World War II were the aggressive actions of Germany, Japan, and Italy coupled with the lack of an Allied response to these actions. Germany began to build up its military, which was done in violation of the Versailles Treaty. In 1936, Germany moved its military into the Rhineland, which also violated the Versailles Treaty. Japan invaded Manchuria in 1931 and invaded China in 1937. Italy invaded Ethiopia in 1935. Germany annexed Austria in 1938. The Allies had little to no response to all of these actions, mainly because the Allies were also dealing with effects of the Great Depression and weren’t prepared to go to war so soon after World War I ended. When Germany wanted to annex the Sudetenland in northwest Czechoslovakia, the leaders of Britain and France agreed to give Germany this land in return for a promise to take no more land, with an agreement known as the Munich Pact.

World War II became much more of a reality in the late 1930s. Germany broke the Munich Pact in 1939 when Germany took the rest of Czechoslovakia. The leaders of Great Britain and France responded by saying any more aggressive actions would lead to war. Germany signed a non-aggression pact with the Soviet Union in August 1939. This agreement would prevent a two-front war for Germany. In September, Germany invaded Poland leading to the start of World War II.

There were many factors that contributed to the outbreak of World War II.