Aftermath

Health and economic effects

..."Strange, friend," I said, "Here is no cause to mourn." "None," said the other, "Save the undone years"...

— Wilfred Owen, Strange Meeting, 1918

No other war had changed the map of Europe so dramatically — four empires disappeared: the German, Austro-Hungarian, Ottoman and the Russian. Four dynasties: the Hohenzollerns, the Habsburg, Romanovs and the Ottomans, together with their ancillary aristocracies, all fell after the war. Belgium and Serbia were badly damaged, as was France with 1.4 million soldiers dead, not counting other casualties. Germany and Russia were similarly affected.
The war had profound economic consequences. Of the 60 million European soldiers who were mobilised from 1914–1918, 8 million were killed, 7 million were permanently disabled, and 15 million were seriously injured. Germany lost 15.1% of its active male population, Austria–Hungary lost 17.1%, and France lost 10.5%. About 750,000 German civilians died from starvation caused by the British blockade during the war. By the end of the war, famine had killed approximately 100,000 people in Lebanon. The best estimates of the death toll from the Russian famine of 1921 run from 5 million to 10 million people. By 1922, there were between 4.5 million and 7 million homeless children in Russia as a result of nearly a decade of devastation from World War I, the Russian Civil War, and the subsequent famine of 1920–1922. Numerous anti-Soviet Russians fled the country after the Revolution; by the 1930s the northern Chinese city of Harbin had 100,000 Russians. Thousands more emigrated to France, England and the United States.

Greek refugees from Smyrna, 1922

American Red Cross nurses tend to 1918 flu pandemic patients in temporary wards set up inside Oakland Municipal Auditorium, 1918.

Diseases flourished in the chaotic wartime conditions. In 1914 alone, louse-borne epidemic typhus killed 200,000 in Serbia. From 1918 to 1922, Russia had about 25 million infections and 3 million deaths from epidemic typhus. Whereas before World War I, Russia had about 3.5 million cases of malaria, its people suffered more than 13 million cases in 1923. In addition, a major influenza epidemic spread around the world. Overall, the 1918 flu pandemic killed at least 50 million people.
Lobbying by Chaim Weizmann and fear that American Jews would encourage the USA to support Germany culminated in the British government's Balfour Declaration of 1917, endorsing creation of a Jewish homeland in Palestine. A total of more than 1,172,000 Jewish soldiers served in the Allied and Central Power forces in World War I, including 450,000 in Czarist Russia and 275,000 in Austria-Hungary.
The social disruption and widespread violence of the Revolution of 1917 and the ensuing Russian Civil War sparked more than 2,000 pogroms in the former Russian Empire, mostly in the Ukraine. An estimated 60,000–200,000 civilian Jews were killed in the atrocities.
In the aftermath of World War I, Greece fought against Turkish nationalists led by Mustafa Kemal, a war which resulted in a massive population exchange between the two countries under the Treaty of Lausanne. According to various sources, several hundred thousand Pontic Greeks died during this period.

Peace treaties and national boundaries

After the war, the Paris Peace Conference imposed a series of peace treaties on the Central Powers. The 1919 Treaty of Versailles officially ended the war. Building on Wilson's 14th point, the Treaty of Versailles also brought into being the League of Nations on 28 June 1919.
In signing the treaty, Germany acknowledged responsibility for the war, agreeing to pay enormous war reparations and award territory to the victors. The "Guilt Thesis" became a controversial explanation of later events among analysts in Britain and the United States. The Treaty of Versailles caused enormous bitterness in Germany, which nationalist movements, especially the Nazis, exploited with a conspiracy theory they called the Dolchstosslegende (Stab-in-the-back legend). The Weimar Republic lost the former colonial possessions and was saddled with accepting blame for the war, as well as paying punitive reparations for it. Unable to pay them with exports (a result of territorial losses and postwar recession), Germany did so by borrowing from the United States. Runaway inflation in the 1920s contributed to the economic collapse of the Weimar Republic and the reparations were suspended in 1931 following the Stock Market Crash in 1929 and the beginnings of the Great Depression worldwide.
Austria–Hungary was partitioned into several successor states, including Austria, Hungary, Czechoslovakia, and Yugoslavia, largely but not entirely along ethnic lines. Transylvania was shifted from Hungary to Greater Romania. The details were contained in the Treaty of Saint-Germain and the Treaty of Trianon. As a result of the Treaty of Trianon, 3.3 million Hungarians came under foreign rule. Although the Hungarians made up 54% of the population of the pre-war Kingdom of Hungary, only 32% of its territory was left to Hungary. Between 1920 and 1924, 354,000 Hungarians fled former Hungarian territories attached to Romania, Czechoslovakia and Yugoslavia.
The Russian Empire, which had withdrawn from the war in 1917 after the October Revolution, lost much of its western frontier as the newly independent nations of Estonia, Finland, Latvia, Lithuania, and Poland were carved from it. Bessarabia was re-attached to the Greater Romania, as it had been a Romanian territory for more than a thousand years.
The Ottoman Empire disintegrated, and much of its non-Anatolian territory was awarded as protectorates of various Allied powers. The Turkish core was reorganised as the Republic of Turkey. The Ottoman Empire was to be partitioned by the Treaty of Sèvres in 1920. This treaty was never ratified by the Sultan and was rejected by the Turkish republican movement, leading to the Turkish Independence War and, ultimately, to the 1923 Treaty of Lausanne.