<P> When the war broke out, much of the fighting was between Western powers, and the immediate casus belli was an assassination . The victim was the heir to the Austro - Hungarian throne, Franz Ferdinand, and he was assassinated on 28 June 1914 by a Yugoslav nationalist named Gavrilo Princip in the city of Sarajevo, at the time part of the Austro - Hungarian Empire . Although Serbia agreed to all but one point of the Austrian ultimatum (it did not take responsibility in planning the assassination but was ready to hand over any subject involved on its territory), Austria - Hungary was more than eager to declare war, attacked Serbia and effectively began World War I. Fearing the conquest of a fellow Slavic Orthodox nation, Russia declared war on Austria - Hungary . Germany responded by declaring war on Russia as well as France, which it feared would ally with Russia . To reach France, Germany invaded neutral Belgium in August, leading Britain to declare war on Germany . The war quickly stalemated, with trenches being dug from the North Sea to Switzerland . The war also made use of new and relatively new technology and weapons, including machine guns, airplanes, tanks, battleships, and submarines . Even chemical weapons were used at one point . The war also involved other nations, with Romania and Greece joining the British Empire and France and Bulgaria and the Ottoman Empire joining Germany . The war spread throughout the globe with colonial armies clashing in Africa and Pacific nations such as Japan and Australia, allied with Britain, attacking German colonies in the Pacific . In the Middle East, the Australian and New Zealand Army Corps landed at Gallipoli in 1915 in a failed bid to support an Anglo - French capture of the Ottoman capital of Istanbul . Unable to secure an early victory in 1915, British Empire forces later attacked from further south after the beginning of Arab revolt and conquered Mesopotamia and Palestine from the Ottomans with the support of local Arab rebels and supported an Arab revolt against the Ottomans centered in the Arabian Peninsula . </P> <P> 1916 saw some of the most ferocious fighting in human history with the Somme Offensive on the Western Front alone resulting in 500,000 German casualties, 420,000 British and Dominion, and 200,000 French casualties . </P> <P> 1917 was a crucial year in the war . The United States had followed a policy of neutrality in the war, feeling it was a European conflict . However, during the course of the war many Americans had died on board British ocean liners sunk by the Germans, leading to anti-German feelings in the U.S. There had also been incidents of sabotage on American soil, including the Black Tom explosion . What finally led to American involvement in the war, however, was the discovery of the Zimmermann Telegram, in which Germany offered to help Mexico conquer part of the United States if it formed an alliance with Germany . In April, the U.S. declared war on Germany . The same year the U.S. entered the war, Russia withdrew . After the deaths of many Russian soldiers and hunger in Russia, a revolution occurred against the Czar, Nicholas II . Nicholas abdicated and a Liberal provisional government was set up . In October, Russian communists, led by Vladimir Lenin rose up against the government, resulting in a civil war . Eventually, the communists won and Lenin became premier . Feeling World War I was a capitalist conflict, Lenin signed a peace treaty with Germany in which it gave up a great deal of its Central and Eastern European lands . </P> <P> Although Germany and its allies no longer had to focus on Russia, the large numbers of American troops and weapons reaching Europe turned the tide against Germany, and after more than a year of fighting, Germany surrendered . </P>

Renaissance technology in western civilization from middle age to 20th century