In the context of the history of the 20th century, the interwar period was the period between the end of the First World War in November 1918 and the beginning of the Second World War in September 1939.
Despite the relatively short period of time, this period represented an era of significant changes worldwide. Petroleum and associated mechanisation expanded dramatically leading to the Roaring Twenties (and the Golden Twenties), a period of economic prosperity and growth for the middle class in North America, Europe and many other parts of the world. Automobiles, electric lighting, radio broadcasts and more became commonplace among populations in the developed world. The indulgences of this era subsequently were followed by the Great Depression, an unprecedented worldwide economic downturn which severely damaged many of the world's largest economies.
The communists in the USSR managed to regain control in Ukraine, Armenia, Azerbaijan and Georgia. Ireland was split, with the larger part being independent of Britain. In the Middle East, Egypt and Iraq gained independence. During the Great Depression, Latin American countries nationalised many foreign companies (particularly American) in a bid to strengthen their local economies. Japanese, German, Italian and Soviet territorial ambitions led to expansions of these empires, which set the stage for the subsequent world war.
Following the Armistice of 11 November 1918 that ended World War I, the years 1919–24 were marked by turmoil as affected regions struggled to recover from the devastation of the First World War and the destabilising effects of the loss of four large historic empires: the German Empire, Austro-Hungarian Empire, Russian Empire and the Ottoman Empire. There were numerous new nations in Eastern Europe, most of them small in size. The United States gained dominance in world finance. Thus, when Germany could no longer afford war reparations to Britain, France and other Allies, the Americans came up with the Dawes Plan and Wall Street invested heavily in Germany, which repaid its reparations to nations that, in turn, used the dollars to pay off their war debts to Washington. By the middle of the decade, prosperity was widespread, with the second half of the decade known, especially in Germany, as the "Golden Twenties".