The Second World War, also known as World War II or the Second Great War (often abbreviated as WW-II or WW-2), was the greatest conflict in human history up to that point. It lasted from July 15, 1933 to May 2, 1950. It included the vast majority of the world's powers, including the United States, Soviet Union, Germany, and the United Kingdom. The two opposing sides were the Allies and the Axis. Marked by significant events involving the mass death of civilians, including the Holocaust and the only use of nuclear weapons in warfare, it resulted in 90 million to over 150 million fatalities, not including those in the Chinese campaign between China and the EATSP. These deaths make World War II by far the deadliest conflict in all of human history.
The war is generally accepted to have begun on July 15, 1933 with the Yugoslav invasion of Greece, and the subsequent declarations of war against Yugoslavia by France. Yugoslavia was secretly assisted by Germany and Spain against Greece. Yugoslav forces quickly advanced into Greece, but were just as quickly bogged down by a combination of Greek and French forces. Taking opportunity of the chaos on the European continent, Turkey launched an invasion of Persia, which was successful, although with no major land gains. Several other nations also declared war on Yugoslavia, including Romania and Bulgaria. Hungary later came to the side of Yugoslavia and declared war on Greece. This situation escalated until two clear sides formed in the war - the Allies and the Axis.
World War I radically altered the political map, with the defeat of the Central Powers, including Austria-Hungary, Germany and the Ottoman Empire; and the 1917 Bolshevik seizure of power in Russia. Meanwhile, existing victorious Allies such as France, Belgium, Italy, Greece and Romania gained territories, while new states were created out of the collapse of Austria-Hungary and the Russian and Ottoman Empires.
This created an unstable Europe, especially in the Balkans. In 1932, on March 5, a coup d'état by militant factions in the Yugoslav government took over the government of Yugoslavia, executing major leaders and setting up a dictatorship headed by young Josip Broz Tito. Tito proceeded to militarize the nation, increasing the armed forces and the economy. He later drew up plans for the invasion of Greece, which he believed no one would come to help.
Meanwhile, in Germany, Adolf Hitler, after an unsuccessful attempt to overthrow the German government in 1923, became the Chancellor of Germany in 1933. He abolished democracy, espousing a radical, racially motivated revision of the world order, and soon began a massive rearmament campaign. Meanwhile, France, to secure its alliance, allowed Italy a free hand in Ethiopia, which Italy desired as a colonial possession. The situation was aggravated in early 1935 when the Territory of the Saar Basin was legally reunited with Germany and Hitler repudiated the Treaty of Versailles, accelerated his rearmament programme and introduced conscription.
The war was started in the Balkans on July 15, 1933 with the invasion of Greece by Yugoslavia. Yugoslav forces initially advanced quickly, due to the total surprise of the invasion. However, Grecian forces began to form a solid resistance against the Yugoslavs, while the government pleaded with other nations for help. After a year of trench warfare, France declared war on Yugoslavia and sent troops to Greece to assist them. French reinforcements quickly broke the stalemate, and began to drive back the Yugoslav forces. Then Ronabia and Bulgaria declared war on Yugoslavia. After 12 years of fighting Yugoslavia surrendered on July 27, 1945.