World War I took place between 1914 and 1918. Although the conflict began in Europe, it ultimately involved countries as far away as the United States and Japan. At the time, the English-speaking world knew it as the “Great War”—the term “World War I” was applied decades later. Historians still actively disagree over the fundamental causes of the war. The period leading up to the war was a complex tangle of diplomacy and political maneuvering—many countries debated over strategies and alliances until nearly the last minute—and the first few weeks of the conflict were similarly chaotic and confusing. However, historians agree nearly unanimously about the war’s consequences: World War I led almost directly to World War II and set the stage for many other important events in the twentieth century.

By conservative estimates, around 9 million soldiers died in battle—many of them defending entrenched front lines that were so stalemated that they rarely moved even a few yards in either direction. Civilian loss of life totaled an additional 13 million. Epidemics of influenza and other diseases, either induced or exacerbated by the war, raised the death toll by at least an additional 20 million. In total, counting battle casualties, civilian deaths, and victims of disease, the loss of life worldwide surpassed 40 million.

Political tensions ran high in early twentieth-century Europe. Abroad, Europe’s great powers were increasingly coming to impasses over the acquisition of new colonies. As the unclaimed lands of the earth ran short, the race to claim them became fiercely competitive. At the same time, the Turkish-ruled Ottoman Empire, which had existed for hundreds of years, was slowly decaying. Greece, Bulgaria, Romania, Serbia, and other southern European nations that had been under Ottoman rule became independent, changing the balance of power in Europe. The many ethnic groups of Austria-Hungary, inspired by these new southern European nations, began to agitate for their own independence. Furthermore, Serbia wanted back the territory of Bosnia-Herzegovina, lost to Austria in a previous war.

At the same time, technological and industrial developments in Europe were advancing with unprecedented speed. Military technology was at the forefront of this trend, and a horrible war using these new weapons was both feared and seen as inevitable. Indeed, World War I turned out to be a showcase of new technologies that would change the nature, speed, and efficiency of warfare in the century to come. Tanks, airplanes, and submarines changed the way wars were fought. Other types of motorized vehicles, such as trucks, cars, and especially trains, vastly improved the speed with which troops and supplies could be deployed and increased the distance over which they could be transported. Guns in all categories, ranging from pistols to major artillery, greatly improved in accuracy and range of fire, enabling armies to fire upon each other across long distances and in some cases without even having to see each other. The machine gun made it possible for a single soldier to effectively take on multiple opponents at once. Chemical warfare was seen on a large scale for the first time, with results so gruesome that most countries vowed never to use such weapons again.

By war’s end, the map of Europe began to resemble the one we know today. The German and Austro-Hungarian empires ceased to exist. Much of eastern Europe, in particular, was redivided along ethno-linguistic lines, and Hungary, Poland, Lithuania, Latvia, Estonia, and Finland all became independent countries. Several other nations were awkwardly combined into the countries of Yugoslavia and Czechoslovakia. A major reorganization of the Near and Middle East also took place following the war, establishing the forerunners of the countries we know today as Armenia, Turkey, Syria, Lebanon, Saudi Arabia, and Iraq.

The aftermath of World War I also marked the practical end of monarchy on the continent and of European colonialism throughout the rest of the world. Most European nations began to rely increasingly upon parliamentary systems of government, and socialism gained increasing popularity. The brutality of the conflict and the enormous loss of human life inspired a renewed determination among nations to rely upon diplomacy to resolve conflicts in the future. This resolve directly inspired the birth of the League of Nations.

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