Because the American people aren't self-sufficient they don't suffer from famine. On the other hand, the bulk of Africans are peasant farmers producing the foods they consume. If drought hits, they starve. They don't have other goods and services to trade for food. The division of labor coupled with free trade allows us to spread the risk of famine.
Free trade is like an insurance policy that pools the risk among many individuals.
It seems odd that so many people want coercive, mandatory social insurance and are opposed to this much fairer system. With free trade a nation receives the benefits of social insurance without the drawbacks of a coercive system. The market solves the problem in several ways. The increased prices encourage people to consume less or purchase foods not in short supply. The increased prices also encourage increased production by farmers.