Half a century since juntas were the rage, generals in the three largest North African countries are trying to bring them back into fashion. In Algeria and Sudan, where popular protests have recently toppled long-reigning tyrants, military cabals are re-emerging from the shadows to bid for power. In Libya, eight unstable years since the fall of a dictator, another aspiring caudillo is trying to seize control by force of arms. The generals-Sudan's Ahmed Awad Ibn Auf, Algeria's Ahmed Gaid Salah and Libya's Khalifa Hifter-should be careful what they wish for. The economic and political challenges that would come with success are monumental, and cannot be solved by military dictatorships. If...