Interwar period can refer to any period between two wars. The Interbellum (1918–1939) is understood to be the period between the end of the Great War or First World War and the beginning of the Second World War in Europe.^{[citation needed]}

This period of history was marked by turmoil, as Europe struggled to recover from the devastation of the First World War. Later a period of considerable prosperity (the Roaring Twenties) followed, but this changed dramatically with the onset of the Great Depression in 1929. It was during this time that the Weimar Republic in Germany gave way to two episodes of political and economic turmoil, the first culminated in the German hyperinflation of 1923 and the failed Beer Hall Putsch of that same year. The second convulsion, brought on by the worldwide depression, resulted in the rise of Nazism. In Asia, Japan became an ever more assertive power, especially with regards to China.

The interwar period was marked by a radical change in the international order, away from the balance of power that had dominated pre–World War I Europe. One main institution intended to bring stability was the League of Nations, created after the First World War with the intention of maintaining world security and peace and encouraging economic growth between member countries. The League was undermined from the start by the non-participation of the United States and the Soviet Union, and subsequently by the bellicosity of Mussolini's Italy, Nazi Germany, and Imperial Japan - leading many to question its legitimacy and effectiveness.

World War I (WWI), which was predominantly called the World War or the Great War from its occurrence until 1939 (World War II), and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918. It involved all the world's great powers, which were assembled in two opposing alliances: the Allies (based on the Triple Entente of the United Kingdom, France and Russia) and the Central Powers (originally centred around the Triple Alliance of Germany, Austria-Hungary and Italy; but, as Austria–Hungary had taken the offensive against the agreement, Italy did not enter into the war). These alliances both reorganised (Italy fought for the Allies), and expanded as more nations entered the war. Ultimately more than 70 million military personnel, including 60 million Europeans, were mobilised in one of the largest wars in history. More than 9 million combatants were killed, largely because of enormous increases in lethality of weapons, thanks to new technology, without corresponding improvements in protection or mobility. It was the sixth-deadliest conflict in world history, subsequently paving the way for various political changes such as revolutions in the nations involved.