Question

what was the cause of world war 2

Answer 1

Short answer: the immediate trigger was Nazi Germany’s invasion of Poland on 1 September 1939. Britain and France then declared war on Germany two days later.

Longer answer — underlying and contributing causes:
- Treaty of Versailles and its aftermath: the harsh terms, territorial losses, reparations, and political instability in Germany created resentment and a fertile ground for extremist politics.
- Economic crisis: the Great Depression of the 1930s increased instability, radicalized politics, and made aggressive expansionist solutions more attractive to some leaders.
- Rise of aggressive authoritarian regimes: fascist Italy, militarist Japan, and especially Nazi Germany pursued expansion, militarization, and revision of the international order.
- Nazi ideology and aims: Hitler’s goals (racial ideology, reversal of Versailles, and "Lebensraum" — territorial expansion in Eastern Europe) drove aggressive policies.
- Failure of collective security: the League of Nations was ineffective, and major powers often failed to check aggression early.
- Appeasement and diplomatic miscalculation: Britain and France’s concessions (e.g., Munich Agreement, 1938) encouraged further aggression by convincing dictators they could seize territory with limited risk.
- Regional conflicts that widened: Japanese expansion in China (from 1937) and Italy’s invasions in Africa helped create a wider global clash.
- Short-term diplomatic moves: the Molotov–Ribbentrop Pact (August 1939), a non‑aggression treaty between Germany and the Soviet Union that secretly divided Eastern Europe, removed the risk of a two‑front war and cleared the way for Germany to attack Poland.

Key prewar events (brief timeline):
- 1931: Japan invades Manchuria.
- 1935–36: Italy invades Ethiopia; Germany remilitarizes the Rhineland.
- 1937: Full-scale Sino‑Japanese War begins.
- 1938: Germany annexes Austria (Anschluss); Munich Agreement allows Germany to seize the Sudetenland.
- March 1939: Germany occupies the rest of Czechoslovakia.
- August 1939: Molotov–Ribbentrop Pact.
- 1 Sept 1939: Germany invades Poland → Britain and France declare war on 3 Sept 1939.

In short, World War II resulted from a mix of long-term political and economic conditions, aggressive ideologies and ambitions, diplomatic failures, and immediate military aggression by Axis powers — with the invasion of Poland serving as the direct spark.