America's enemies have a tendency to underestimate the United States and its people. One of the initial reactions to the terrorist attacks on New York City and Washington, D.C., was to say that it was a second Pearl Harbor. Those who said this probably did not realize the appropriateness of the comparison.
The situation is reminiscent of U.S.-Japanese relations in the 1930s and during the Pacific War. The Japanese underestimated Americans because of what they had seen throughout the interwar period: the Western democracy as a whole was either reluctant or ineffectual to stop aggressions by some rogue states. Italy's ambitions in Africa were not checked; Germany was appeased; and Japan could wage wars in Asia without a fear of intervention. The Japanese wrongly judged that the West would not dare go to war against them unless directly attacked. As the 1930s roared on, they even let themselves believe that the decadent Americans did not have the stomach for a fight that could last for years.