The Central African Republic — wedged in the middle of the African continent between the Republic of the Congo, the Democratic Republic of the Congo, Chad, Cameroon, Sudan and South Sudan — often falls short of satisfying the formal definition of a state. It has little means to control the violence within its borders, and its reputation in recent years has been that of a failing state rife with unrest and conflict amid a proliferation of armed rebel groups. At the heart of these problems is the Central African Republic's geography. Most of the country lies within Africa's savannah zone, on the border between the semi-arid Sahel and the intertropical convergence zone, which begins south of the capital, Bangui. The savannah zone's soils, composed of limestone sand, are not conducive to agriculture.