The Indian Army (IA), often known since 1947 (but rarely during its existence) as the British Indian Army to distinguish it from the current Indian Army, was the principal military of the British Indian Empire before its decommissioning in 1947. It was responsible for the defence of both British Indian Empire and the princely states, which could also have their own armies. The Indian Army was an important part of the British Empire's forces, both in India and abroad, particularly during the First World War and the Second World War.
The term "Indian Army" appears to have been first used informally, as a collective description of the Presidency armies (the Bengal Army, the Madras Army and the Bombay Army) of the Presidencies of British India, particularly after the Indian Rebellion. The first army officially called the "Indian Army" was raised by the government of India in 1895, existing alongside the three long-established presidency armies. However, in 1903 the Indian Army absorbed these three armies. The Indian Army should not be confused with the "Army of India" (1903–1947) which was the Indian Army itself plus the "British Army in India" (British units sent to India).
The Indian Army has its origins in the years after the Indian Rebellion of 1857, often called the Indian Mutiny in British histories, when in 1858 the Crown took over direct rule of British India from the East India Company. Before 1858, the precursor units of the Indian Army were units controlled by the Company and were paid for by their profits. These operated alongside units of the British Army, funded by the British government in London.
The armies of the East India Company were recruited primarily from Muslims in the Bengal Presidency, which consisted of Bengal, Bihar and Uttar Pradesh, and high caste Hindus recruited primarily from the rural plains of Oudh. Many of these troops took part in the Indian Mutiny, with the aim of reinstating the Mughal Emperor Bahadur Shah II at Delhi, partly as a result of insensitive treatment by their British officers.
The meaning of the term "Indian Army" has changed over time: