In India, a caste is a (usually endogamous) social group where membership is decided by birth. Castes often have related political preferences. Broadly, Indian castes are divided into the Forward Castes, Other Backward Classes, Scheduled Castes, and Scheduled Tribes, though Indian Christians and Indian Muslims can also function as castes. In the era of British India, the British institutionalised caste into India's governmental institutions. However, by the 1990s, there was a social movement to empower the lower castes.