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.
Politically, this era coincided with the rise of communism, starting in Russia with the October Revolution, at the end of World War I, and ended with the rise of fascism, particularly in Germany. China was in the midst of long period of instability and civil war between the Kuomintang and the Communist Party of China. The Empires of Britain, France and others faced challenges as imperialism was increasingly viewed negatively in Europe, and independence movements in British India, French Vietnam, Ireland and other regions gained momentum. The former Ottoman, Austro-Hungarian and German Empires were dismantled, with the Ottoman and German Empire's colonies redistributed among the Allies. The far western part of the Russian Empire broke away: Estonia, Finland, Latvia, Lithuania and Poland became independent nation states,while Bessarabia (the Republic of Moldova) chose to reunify with Romania. However, the Communists in Moscow 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 Russian 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".
The important stages of interwar diplomacy and international relations included resolutions of wartime issues, such as reparations owed by Germany and boundaries; American involvement in European finances and disarmament projects; the expectations and failures of the League of Nations; the relationships of the new countries to the old; the distrustful relations of the Soviet Union to the capitalist world; peace and disarmament efforts; responses to the Great Depression starting in 1929; the collapse of world trade; The collapse of democratic regimes one by one; the growth of economic autarky; Japanese aggressiveness toward China; Fascist diplomacy, including the aggressive moves by Mussolini's Italy and Hitler's Germany; the Spanish Civil War; the appeasement of Germany's expansionist moves toward the Rhineland, Austria, and Czechoslovakia, and the last, desperate stages of rearmament as the second world war increasingly loomed.
The "Roaring Twenties" highlighted novel and highly visible social and cultural trends and innovations. These trends, made possible by sustained economic prosperity, were most visible in major cities like New York, Chicago, Paris, Berlin and London. The Jazz Age began and Art Deco peaked. For women, knee-length skirts and dresses became socially acceptable, as did bobbed hair with a marcel wave. The women who pioneered these trends were frequently referred to as flappers. Not all was new: “normalcy” returned to politics in the wake of hyper-emotional wartime passions in the United States, France, and Germany. The leftist revolutions in Finland, Poland, Germany, Austria, Hungary and Spain were defeated by conservatives, but succeeded in Russia, which became the base for Soviet Communism. In Italy the fascists came to power under Mussolini after threatening a march on Rome.