Foreign affairs are not a series of disconnected episodes. They are a test of whether nations learn from history and act with foresight. The United States has often failed that test. It forgets that unchecked aggression leads to wider wars and that removing governments without building new authority invites chaos. Russia’s invasion of Ukraine, Iran’s destabilising role in the Middle East and the collapse of Libya and Afghanistan all testify to what happens when those lessons are ignored. China,...