"Early and mid 20th century Muslim historians, such as Hashimi in 1927 and Qureshi in 1962, proposed that "caste system was established before the arrival of Islam", and it and "a nomadic savage lifestyle" in the northwest Indian subcontinent were the primary cause why Sindhi non-Muslims "embraced Islam in flocks" when Arab Muslim armies invaded the region.According to this hypothesis, the mass conversions occurred from the lower caste Hindus and Mahayana Buddhists who had become "corroded from within by the infiltration of Hindu beliefs and practices".