World War I broke out on July 28, 1914, when Austria-Hungary declared war on Serbia. There had been conflict between the two countries but never seemed to be significant until it started to spread rapidly. Germany, Russia, Great Britain, and France were all brought into the war, mainly because they were involved in treaties that basically forced them to defend other countries. Western and eastern fronts began to open along the borders of Germany and Austria-Hungary.The first month of war was mainly lots of harsh attacks and quick troop movements on both fronts. In the west, Germany attacked Belgium and France. In the east, Russia attacked Germany and Austria-Hungary. In the south, Austria-Hungary invaded Serbia. In late 1914, the Ottoman Empire was brought into the war too, because Germany made Russia think that Turkey had attacked it. The outcome of this is that most of 1915 consisted of Allied actions against the Ottomans in the Mediterranean. First, Britain and France attempted and failed to attack the Dardanelles. After this campaign the British invasion of the Gallipoli Peninsula took place. Britain also started a separate campaign against the Turks in Mesopotamia. Although the British had some victories in Mesopotamia, most of their invasions and campaigns resulted in failure. During 1916 and 1917, trench warfare continued in the east and the west. Soldiers fought from dug-up trenches in the ground and were able to use machine guns, heavy artillery, and chemical weapons while using the trench as protection. Millions of soldiers died in brutal conditions because of trench warfare but neither side had any major success or gained any advantage. In 1917 two important developments occurred. In early April, the United States was mad about attacks on its ships in the Atlantic, and decided to declare war on Germany. In November, the Bolshevik Revolution forced Russia to pull out of the war. Despite the fact that both sides launched new armies in 1918 in a desperate attempt to win the war, both reforms failed. Soldiers became exhausted and tens of thousands were dying due to several causes. A deadly outbreak of influenza was one of many causes of the mass deaths. Eventually, the governments of both Germany and Austria-Hungary began to lose control as both countries suffered from difficulties within their militaries. The war ended in late 1918, when the Central Powers signed agreements one by one. Germany was the last to agree, signing on November 11, 1918. As a result of these agreements, Austria-Hungary was broken up into several smaller countries. Germany, under the Treaty of Versailles, was punished by huge economic decline, territorial loss of land, and strict limits on its rights to develop an army.