Attacks by Islamic extremists are rampant in Africa's Sahel

DAKAR, Senegal — Extremist attacks in Sahel, an arid swath of land south of the Sahara in Africa, have proliferated in recent months: Last week, Islamic militants attacked Bamako, the capital of Mali, for the first time in almost a decade, demonstrating their capacity to carry out large scale assaults. And last month, at least 100 villagers and soldiers were killed in central Burkina Faso during a weekend attack on a village by al-Qaida-linked jihadis, as they were forcibly helping security forces...