World War I was important for India's nationalist movement. Indians of all persuasions overwhelmingly supported Great Britain and the Allied cause during the war. Nearly 800,000 Indian soldiers plus 500,000 noncombatants served in Europe and the Middle East.
Communal relations between Hindus and Muslims took several turns between the passage of the India Councils Act in 1909 and 1919. The reunion of Bengal in 1911 (which canceled its partition into two provinces) pleased the Hindus but antagonized the Muslims.
The All-India Muslim League began to attract younger and bolder leaders, most notably a brilliant lawyer named Mohammad Ali Jinnah (1876–1946). Similarly Mohandas K. Gandhi (1869–1948) and Jawaharlal Nehru (1889–1967) emerged as leaders of the Indian National Congress.
Many in India's Muslim minority became concerned with the ultimate fate of the Muslim Ottoman Empire, which fought in the opposing Central Powers camp. World War I also aroused both the congress and the league to demand significant constitutional reforms from Britain. In 1916 they concluded a Congress League Scheme of Reforms, known as the Lucknow Pact.
It made wide-ranging demands for greater self-government, equality of Indians with other races throughout the British Empire and Commonwealth (in response to racial discrimination in South Africa and Canada), and greater opportunities for Indians in the armed forces of India.
In response, the new secretary of state for India, Edwin Montagu, officially announced the British government's commitment to "the gradual development of self-governing institutions with a view to the progressive realization of responsible government in India" in August 1917.
He then toured India, met with Indian leaders, and together with Viceroy Lord Chelmsford drafted a Report for Indian Constitutional Reform in 1918, popularly called the Montagu Chelmsford Report. A modified version of the report was embodied in the Government of India Act of 1919.
It introduced partial self-government to India's nine provinces in a system called dyarchy, whereby elected representatives controlled the departments of agriculture, sanitation, education, and so on, while the British-appointed governor and his advisers retained control of finance, the police, prisons, and relief.
This was intended as a step toward complete responsible government. The viceroy, however, retained control of the central government, and the role of the mostly elected bicameral legislature remained advisory. The electorate was expanded, and separate electorates (Muslims elected their own representatives) were kept in place, on Muslim insistence.
The Government of India Act was a significant advance in India's freedom movement. Others included a separate Indian delegation to the Paris Peace Conference in 1919, in the same manner as the self-governing dominions (Canada, Australia, New Zealand, and South Africa). India also became a member of the League of Nations.
But these advances did not satisfy Indian nationalists, who were inflamed by the continuation of wartime laws that abridged civil freedoms, and acts of peaceful and violent resistance continued. Hindu-Muslim accord continued during the Khalifat movement, when Indians supported the Ottoman emperor's religious leadership as caliph of Islam.
The cooperation collapsed when Mustafa Kemal Atatürk established a republic in Turkey and abolished the caliphate in 1923 and also due to increasing competition between the two communal groups for power in a future independent India.