A Deadly War
Many of the deadliest battles in history occurred in this war. See Ypres, Vimy Ridge, Marne, Cambrai, Somme, Verdun, Gallipoli. See Wars of the 20h Century for various totals given for the number that died in this war. For instance, is it proper to consider the Influenza pandemic (see below) as part of the overall death count for the war, given the important part the War played in its transmission?
Revolutions
Perhaps the single most important event precipitated by the privations of the war was the Russian Revolution. Socialist and explicitly Communist uprisings also occurred in many other European countries from 1917 onwards, notably in Germany and Hungary. As a result of the Bolsheviks’ failure to cede territory, German and Austrian forces defeated the Russian armies, and the new communist government signed the Treaty of Brest-Litovsk in March 1918. In that treaty, Russia renounced all claims to Finland, Latvia, Lithuania, Poland (specifically, the formerly Russian-controlled Congress Poland of 1815), and Ukraine, and it was left to Germany and Austria-Hungary “to determine the future status of these territories in agreement with their population.”
Influenza pandemic
A separate, but related event was the great influenza pandemic. A new strain of Influenza, originating in the U.S.A. (but misleadingly known as “Spanish Flu”) was accidentally carried to Europe with the American forces. The disease spread rapidly through both the continental U.S. and Europe, reaching, eventually, around the globe. The exact number of deaths is unknown, but in excess of 20 million people worldwide is not considered an overestimate.
Social trauma: The experiences of the war lead to a sort of collective national trauma afterward for all the participating countries. The optimism of 1900 was entirely gone and those who fought in the war became what is known as “the Lost Generation” because they never fully recovered from their experiences. This was especially acute in France where a huge number of young men were killed or injured during the conflict. For the next few years the nation became obsessive in its mourning and thousands of memorials were erected, one for each village in France.
Geopolitical Consequences
Nearly 15 percent of the land area of the German Empire was ceded at Allied insistence to various countries. The largest confiscated part of Germany was given to Poland; this part was called the “Polish Corridor” because of its position between East Prussia and the rest of Germany. In addition, the western powers helped Poland gain another huge chunk of land in western Ukraine. Britain and France occupied the vast majority of former German and Ottoman colonies as “League of Nations mandates”.
Russia also lost substantial land. The countries of Lithuania, Latvia, and Estonia were created to accommodate ethnic groups. Also, land was taken for addition to Poland, and Romania.
The Austro-Hungarian Empire was broken into many pieces. The new republics of Austria and Hungary were established, disavowing any continuity with the empire. Bohemia, Moravia, and Slovakia formed the new Czechoslovakia. Galicia was transferred to Poland and South Tyrol and Trieste went to Italy. Bosnia-Herzegovina, Croatia, Slovenia, and Vojvodina were joined with Serbia and Montenegro to form the Kingdom of the Serbs, Croats and Slovenes, later Yugoslavia. Transylvania became part of Romania.
Because of the intermixed population and partly because of the interests of great powers, the new borders did not always follow ethnic divisions. The new states of eastern Europe nearly all had large national minorities. Hundreds of thousands of Germans continued to live in the newly created countries. A quarter of ethnic Hungarians found themselves living outside of Hungary.
Less concrete changes include the growing assertiveness of Commonwealth nations. Battles such as Gallipoli for Australia and New Zealand, and Vimy Ridge for Canada led to increased national pride and a greater reluctance to remain subordinate to Britain, leading to the growth of diplomatic autonomy in the 1920s.
Also extremely important was the participation of French colonial troops from Indochina, North Africa, and Madagascar without whom France might well have fallen. When these soldiers returned to their homelands and continued to be treated as second-class citizens, many became the nucleus of pro-independence groups.