Russia decided to intervene to protect Serbia, a small fellow Slavic nation, despite there being no treaty requiring Russia to do so. The Tsar had the support of the President of France, who otherwise was hardly involved. Russia mobilized its army against Austria-Hungary. France mobilized its army. Germany declared war on Russia and France, and invaded France through Belgium. Britain had an understanding and military and naval planning agreements with France, but no formal treaty obligations. Britain did have a treaty obligation toward Belgium, and as a result Britain joined France and Russia (the Allies) and declared war on Germany and Austria-Hungary (the Central Powers). Japan, allied with Britain, joined the Allies. The Ottoman Empire (Turkey) joined the Central Powers. Italy, instead of joining Germany and Austria-Hungary with whom it had treaties, entered the war on the side of the Allies in 1915. The United States tried unsuccessfully to broker peace negotiations, and entered the war on the Allied side in April 1917. After very heavy losses on both sides, the Allies were decisively victorious, and divided the spoils of victory, such as the German colonies and much of the territory of the Ottoman Empire. The Austro-Hungarian, German, Russian and Ottoman Empires disintegrated.