Merchants and traders introduced Islam to West Africa in the eighth century. Virtually all of the country is Sunni Muslim; the Tijani and Qadiri Sufi brotherhoods are predominant. Upon independence from the French (1960), the country's founders promoted a common Islamic culture to supplant ethnic constructions of national identity. The combined effects of the Sahara war, over twenty years of increasing drought, and resulting urbanization brought heightened internal tensions. Growing foreign debt is the most urgent domestic concern. Most threats to internal security are based on ethnic or racial tensions.