Ottoman rule over Iraq lasted until World War I, when the Ottomans sided with Germany and the Central Powers. In the Mesopotamian campaign against the Central Powers, British forces invaded the country and suffered a defeat at the hands of the Turkish army during the Siege of Kut (1915–16). However the British finally won in the Mesopotamian Campaign with the capture of Baghdad in March 1917. During the war the British employed the help of a number of Assyrian, Armenian and Arab tribes against the Ottomans, who in turn employed the Kurds as allies. After the war the Ottoman Empire was divided up, and the British Mandate of Mesopotamia was established by League of Nations mandate. Britain imposed a Hāshimite monarchy on Iraq and defined the territorial limits of Iraq without taking into account the politics of the different ethnic and religious groups in the country, in particular those of the Kurds and the Christian Assyrians to the north. During the British occupation, the Kurds fought for independence, and the British employed Assyrian Levies to help quell these insurrections. Iraq also became an oligarchy government at this time.