The National Interest
Spring 2002

The Best Defense

by Barry Posen

 

The concept of "unbalanced multipolarity" is one of Mearsheimer’s key theoretical innovations. It is Mearsheimer’s story of Europe’s great wars. In contrast to defensive realists, Mearsheimer does not believe that there is enough variation in the inherent defensive or offensive possibilities of military technology in any given era to affect significantly the competitive behavior of states. Defensive realists believe that competition among land powers will be muted when the defense has the advantage. Mearsheimer believes that land power is land power, and that the power to defend and the power to attack are pretty much the same. To make this point, he carefully measures the power of states since the French Revolution. He shows convincingly that the great aspiring hegemons—Napoleonic France, Wilhelmine Germany, Nazi Germany and Soviet Russia—were significantly superior to their immediate neighbors when they embarked on their ambitious careers. Moreover, he shows that the young United States embarked on a similar career in North America, and for similar reasons. He notes, however, that the United States is modern history’s only successful regional hegemon; all others failed. . . .

Mearsheimer has made a significant contribution to our understanding of the behavior of great powers—especially great land powers. For the most part, their security concerns are not easily satisfied. Their basic tendency is to expand to dominate their immediate environment, meaning, for the most part, the territories around them. They do this for security reasons: one does not need a hyper-active genius like Napoleon, an imaginative but adolescent atavist like Kaiser Wilhelm II, or a monster like Adolf Hitler to get hegemonic wars. One only needs unbalanced multipolarity amid the massive power of the states these men led. Stated baldly this argument is overdrawn, but it serves an important theoretical purpose: to show that all aspiring hegemons have in common a significant military advantage over their neighbors. Mearsheimer successfully demonstrates that the great land powers do bid for hegemony and that "land power is the main instrument for winning wars." He is twice correct, but it would have been helpful had he wrestled theoretically with the fact that the "land powers" seldom win their great hegemonic wars. Napoleonic France, Wilhelmine Germany, Nazi Germany and the Soviet Union in the Cold War are 0 for 4, and the great sea powers have been central to bringing them down. . . .