The United States has long operated under a seductive strategic fantasy. Remove the leader of an adversary organization, whether a drug cartel, a terrorist group, or a sovereign state, and that organization will collapse, enabling American interests to fill the...

In 2011, the world welcomed its newest country. Fifteen years later, South Sudan is less a symbol of self-determination than a case study in state failure. Its politics remain dominated by factional strongmen, its economy is almost entirely dependent on oil, and the...