The Second World War was not the automatic result of one treaty or one man's personality. It emerged from the interaction of the post-1918 settlement, economic and political crises, the weakness of international institutions and deliberate expansion by Nazi Germany, Fascist Italy and imperial Japan. The immediate European war began with Germany's invasion of Poland in September 1939, but the route to that decision stretched back two decades.
The aftermath of the First World War
The First World War destroyed the German, Austro-Hungarian, Ottoman and Russian empires and left governments with heavy debts, traumatised populations and disputed borders. The Treaty of Versailles transferred territory, restricted Germany's armed forces and required reparations. Many Germans regarded the settlement as humiliating, but the Weimar Republic was not doomed from birth and the treaty did not dictate a Nazi future.
The settlement created or enlarged states in central and eastern Europe while leaving minority populations on different sides of new borders. The League of Nations embodied hopes for collective security, yet it lacked its own forces and depended on member governments. The United States did not join, and Britain and France were often unwilling to accept the cost of decisive enforcement.
Depression, dictatorship and racial ideology
The global economic crisis after 1929 produced unemployment, banking failures and political polarisation. In Germany, support grew for parties that rejected parliamentary democracy. Adolf Hitler became chancellor in January 1933 and rapidly destroyed constitutional government, but conservative elites, officials and military leaders helped make that seizure of power possible.
Nazi foreign policy was inseparable from racial ideology. Hitler sought to overturn Versailles, unite ethnic Germans under his rule and conquer land in eastern Europe. Rearmament, withdrawal from international agreements and persecution at home were parts of the same dictatorship, not separate policies.
The failure of collective security
Japan seized Manchuria in 1931 and Italy invaded Ethiopia in 1935. International protests and sanctions failed to reverse either conquest. Germany remilitarised the Rhineland in 1936, intervened alongside Italy in the Spanish Civil War and absorbed Austria in March 1938. Each success increased Hitler's confidence that his opponents would not fight.
Britain and France pursued appeasement partly because the memory of 1914–18 was so powerful. Leaders also feared aerial bombing, doubted their military readiness, faced imperial commitments and believed that some German complaints about Versailles were legitimate. Appeasement was therefore more than cowardice, but its concessions did not satisfy a regime committed to expansion.
Czechoslovakia and Munich
Hitler demanded the Sudetenland, a fortified border region of Czechoslovakia with a large German-speaking population. At Munich in September 1938, Britain and France accepted German annexation without Czechoslovak participation. Prime Minister Neville Chamberlain hoped the agreement secured a general settlement; it instead weakened a potential German opponent and encouraged further demands.
Germany occupied Prague in March 1939, showing that Hitler's objectives extended beyond self-determination for German speakers. Britain and France guaranteed Poland. Both accelerated military preparations, but diplomacy with the Soviet Union remained hesitant and mistrustful.
Poland and the decision for war
In August 1939 Germany and the Soviet Union signed a non-aggression pact with secret arrangements to divide spheres of influence in eastern Europe. The agreement reduced Hitler's immediate fear of a two-front war and allowed Stalin to buy time while extending Soviet control westward.
German forces invaded Poland on 1 September. Britain and France declared war on 3 September after their ultimatum expired. Responsibility for the European war rests above all with the Nazi leadership's choice of conquest, while the wider explanation includes the international failures that made aggression progressively easier.
Why It Matters
Understanding the causes prevents a complex breakdown from being reduced to one treaty or one conference. It also keeps responsibility clear: conditions created opportunity, but leaders still made choices.