Concerns over Berlin and Cuba led American forces to confront Soviet forces in situations in which a misstep, a rash action by an aggressive or nervous officer, might have led to war. Nikita Khrushchev provoked each of these crises. The Berlin crisis he created in 1958 provides a useful example of how he functioned. The revival of German power in the late 1950s, and evidence of growing German influence within the Western alliance, worried Soviet analysts. By the spring of 1960, the American government knew unequivocally, from intelligence gathered by U-2 over-flights of the Soviet Union, that Khrushchev's claims of missile superiority were unwarranted. The Cuban Communist party was legalized and its members began to play a role, although relatively minor, in the implementation of Fidel Castro's programs. Air raids by CIA-operated bombers had failed to eliminate the tiny Cuban air force but had prompted a Cuban military alert and protest to the United Nations.