On other continents, many people live more closely packed against their neighbors — including potential competitors or enemies. Setting out from Atlanta or St. Louis or Denver, you can drive all day and into the night without reaching an international border. From Munich, there are five within 150 miles.

This leads to different ways of perceiving the world. Successful countries in Europe are those that have mastered the art of delicately balancing rival interests. Experience has taught them to seek long-term security. That requires accommodating neighbors whenever possible, not insulting, confronting, or punishing them.

During the Cold War, competition over ideology was so intense that it seemed every other conflict in Europe had disappeared. The first sign that this assumption was wrong came in the Yugoslavia wars of the 1990s, which showed the persistence of ethnic nationalism. Now age-old patterns of alliance and rivalry are re-emerging in Europe. Managing old resentments and enmities is a delicate job — especially in Europe, where modern history testifies to how horribly things can go wrong when conflict breaks out. Fortunately, geography has given Europeans an instinct to cooperate and compromise.

Americans, unchallenged masters of an enormous continent, never had to develop this instinct.