Chad has over 100 languages spoken within its borders. French and Arabic are the official languages, though Chadian Arabic has become a lingua franca due to Arab traders. Chad has a presidential republic political system with executive power held by the government and legislative power shared between government and parliament. The population is religiously diverse, with a majority of Muslims following a moderate Sufi sect and Roman Catholics as the largest Christian group. Chad's geography spans from savanna in the south to the Sahara Desert in the north, with N'Djamena as the capital city. Agriculture, particularly livestock herding and formerly cotton, dominates Chad's economy.