Interwar period
In the history of the 20th century, the interwar period, also known as the interbellum, lasted from 11 November 1918 to 1 September 1939 – from the end of World War I to the beginning of World War II. It was relatively short, yet featured many social, political, military, and economic changes throughout the world. Petroleum-based energy production and associated mechanisation led to the prosperous Roaring Twenties, a time of social and economic mobility for the middle class. Automobiles, electric lighting, radio, and more became common among populations in the first world. The era's indulgences were followed by the Great Depression, an unprecedented worldwide economic downturn that severely damaged many of the world's largest economies.
Politically, the era coincided with the rise of communism, starting in Russia with the October Revolution and Russian Civil War, at the end of WWI, and ended with the rise of fascism, particularly in Germany and Italy. China was in the midst of a half-century of instability and the Chinese Civil War between the Kuomintang, the Chinese Communist Party, and many warlords. The empires of Britain, France, and others faced challenges as imperialism was increasingly viewed negatively and independence movements emerged in many colonies; in Europe, after protracted low-level fighting most of Ireland became independent.
The Russian, Ottoman, Austro-Hungarian, and German Empires were dismantled, with the Ottoman territories and German colonies redistributed among the Allies, chiefly Britain and France. The western parts of the Russian Empire, Estonia, Finland, Latvia, Lithuania, and Poland became independent nations in their own right, and Bessarabia chose to reunify with Romania.
In Russia, the Bolsheviks managed to regain control of Belarus and Ukraine, Central Asia, and the Caucasus, forming the Soviet Union. In the Near East, Egypt and Iraq gained independence. During the Great Depression, countries in Latin America nationalised many foreign companies in a bid to strengthen their own economies. The territorial ambitions of the Japanese, Italians, and Germans led to the expansion of their domains. The Soviets additionally harbored territorial ambitions during this period and sought to revise the post-WWI settlements.
Militarily, there was a markedly rapid advance in technology in the period, alongside lessons learned from WWI and new strategic and tactical innovations were catalysed. While the period would largely see a continuation of the development of the technologies pioneered in WWI, debates emerged as to the most effective use of these advancements. On land, discussions focused on how armoured, mechanised, and motorised forces should be employed, particularly in-relation to the traditional branches of the regular infantry, horse cavalry, and artillery. In the air, the question of allocating air forces to strategic bombing versus dedicating such forces to frontline close air support was the primary contention, with some arguing that interceptor development was outpacing bombers, and others maintaining that "the bomber will always get through." In the naval sphere, the primary question was whether battleships would maintain their dominance of the seas or be rendered virtually obsolete by naval aviation.
Via the events of WWII, the military deliberations and controversies characteristic of the interwar period ultimately were resolved, which served as a foundation for many of the tenets, doctrines, and strategies of modern warfare. Overall, the innovations of WWI and the interwar period would see a shift away from traditional line- and front-based warfare and towards a significantly more mobile, mechanised, and asymmetric form of combat.
Turmoil in Europe
After the Armistice of Compiègne on 11 November 1918, which ended the fighting of World War I, the years 1918–1924 were marked by turmoil as the Russian Civil War continued to rage on, and Eastern Europe struggled to recover from the devastation of the First World War and the destabilising effects of not just the collapse of the Russian Empire, but the destruction of the German, Austro-Hungarian, and Ottoman Empires, as well. There were numerous new or restored countries in Southern, Central, and Eastern Europe, some small in size including Lithuania and Latvia, and some larger, such as Poland and the Kingdom of Serbs, Croats, and Slovenes. The United States gained dominance in world finance. Thus, when Germany refused to pay further war reparations to Britain, France and other former members of the Entente, 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 as the Roaring Twenties.International relations
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 efforts at economic autarky; Japanese aggressiveness toward China, occupying large amounts of Chinese land, as well as border disputes between the Soviet Union and Japan, leading to multiple clashes along the Soviet and Japanese occupied Manchurian border; fascist diplomacy, including the aggressive moves by Mussolini's Italy and Hitler's Germany; the Spanish Civil War; Italy's invasion and occupation of Abyssinia in the Horn of Africa; the appeasement of Germany's expansionist moves against the German-speaking nation of Austria, the region inhabited by ethnic Germans called the Sudetenland in Czechoslovakia, the remilitarisation of the League of Nations demilitarised zone of the German Rhineland region, and the last, desperate stages of rearmament as the Second World War increasingly loomed.Disarmament was a very popular public policy. However, the League of Nations played little role in this effort, with the United States and Britain taking the lead. U.S. Secretary of State Charles Evans Hughes sponsored the Washington Naval Conference of 1921 in determining how many capital ships each major country was allowed. The new allocations were actually followed and there were no naval races in the 1920s. Britain played a leading role in the 1927 Geneva Naval Conference and the 1930 London Conference that led to the London Naval Treaty, which added cruisers and submarines to the list of ship allocations. However the refusal of Japan, Germany, Italy and the USSR to go along with this led to the meaningless Second London Naval Treaty of 1936. Naval disarmament had collapsed and the issue became rearming for a war against Germany and Japan.
Roaring Twenties
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 including New York City, 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 young women who pioneered these trends were called "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 and Marxism–Leninism. In Italy, the National Fascist Party came to power under Benito Mussolini after threatening a March on Rome in 1922.Most independent countries enacted women's suffrage in the interwar era, including Canada in 1917, Britain in 1918, and the United States in 1920. There were a few major countries that held out until after the Second World War. Leslie Hume said,
In Europe, according to Derek Aldcroft and Steven Morewood, "Nearly all countries registered some economic progress in the 1920s and most of them managed to regain or surpass their pre-war income and production levels by the end of the decade." The Netherlands, Norway, Sweden, Switzerland, and Greece did especially well, while Eastern Europe did poorly, due to the First World War and Russian Civil War. In advanced economies the prosperity reached middle class households and many in the working class with radio, automobiles, telephones, and electric lighting and appliances. There was unprecedented industrial growth, accelerated consumer demand and aspirations, and significant changes in lifestyle and culture. The media began to focus on celebrities, especially sports heroes and movie stars. Major cities built large sports stadiums for the fans, in addition to palatial cinemas. The mechanisation of agriculture continued apace, producing an expansion of output, which lowered prices, and made many farm workers redundant. Often they moved to nearby industrial towns and cities.
Great Depression
The Great Depression was a severe worldwide economic depression that took place after 1929. The timing varied across nations; in most countries it started in 1929 and lasted until the late 1930s. It was the longest, deepest, and most widespread depression of the 20th century. The depression originated in the United States and became worldwide news with the stock market crash of 29 October 1929. Between 1929 and 1932, worldwide GDP fell by an estimated 15%. By comparison, worldwide GDP fell by less than 1% from 2008 to 2009 during the Great Recession. Some economies started to recover by the mid-1930s. However, in many countries, the negative effects of the Great Depression lasted until the beginning of World War II.The Great Depression had devastating effects in countries both rich and poor. Personal income, tax revenue, profits, and prices dropped, while international trade plunged by more than 50%. Unemployment in the United States rose to 25% and in some countries rose as high as 33%. Prices fell sharply, especially for mining and agricultural commodities. Business profits fell sharply as well, with a sharp reduction in new business starts.
Cities all around the world were hit hard, especially those dependent on heavy industry. Construction was virtually halted in many countries. Farming communities and rural areas suffered as crop prices fell by about 60%. Facing plummeting demand with few alternative sources of jobs, areas dependent on primary sector industries such as mining and logging suffered the most.
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 the same year. The second convulsion, brought on by the worldwide depression and Germany's disastrous monetary policies, resulted in the further rise of Nazism. In Asia, Japan became an ever more assertive power, especially with regard to China.