In a move that could reshape the security landscape of the West African Sahel, the leaders of Mali, Burkina Faso and Niger announced that they had signed a joint defense pact called the “Sahel Alliance."

Gabon’s military coup, which followed similar events in Mali, Burkina Faso, Chad, Sudan and Niger, has sparked speculation about the emergence of an “African Spring” — a wave of popular uprisings against authoritarian regimes across the continent.

A group of senior army officers in Gabon declared a coup last week, seizing control of the national television and announcing the end of the rule of President Ali Bongo, who won a third term in a disputed election on August 30.