The Sati practice is considered to have originated within the warrior aristocracy in the Hindu society, gradually gaining in popularity from the 10th century AD and spreading to other groups from the 12th through 18th century AD. The earliest Islamic invasions of South Asia have been recorded from early 8th century CE, such as the raids of Muhammad bin Qasim, and major wars of Islamic expansion after the 10th century. This chronology has led to the theory that the increase in sati practice in India may be related to the centuries of Islamic invasion and its expansion in South Asia. Daniel Grey states that the understanding of origins and spread of sati were distorted in the colonial era because of a concerted effort to push "problem Hindu" theories in the 19th and early 20th centuries.