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 the Arab revolt and conquered Mesopotamia and Palestine from the Ottomans with the support of local Arab rebels. The British Empire also supported an Arab revolt against the Ottomans that was centered in the Arabian Peninsula. 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 casualties, and 200,000 French casualties. 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.