The Allies, led by Britain, France, Russia, Italy, and later the United States, defeated the CentralPowers, led by Germany,Austria-Hungary, and Turkey.
The immediate trigger for the war was the assassination of Archduke Franz Ferdinand of Austria by Serbian nationalists, but the war was a result of tensions that had been building up for decades between the major powers.
Germany had to pay reparations (compensation) to other countries involved in the war.
The League of Nations was established as an international organization aimed at preventing future wars through collective security measures.
The Treaty of Versailles imposed harsh penalties on Germany, including loss of territory, heavy financial reparations, and restrictions on its military capabilities.
Many Germans felt humiliated and resentful towards the treaty's provisions, leading to anger and frustration among the population.
The Great Depression, which began in 1929, contributed to growing economic instability and political unrest in Europe.