Which of these measures did Americans fear was likely to lead to nuclear war with the Soviet Union?

U. S. spy flights over Cuba

Cuban refugees coming to the United States

a quarantine of Cuba in international waters

U. S. demands that Soviets dismantle their missiles

The US established a naval blockade on October 22 to prevent further missiles from reaching Cuba; Oval Office tapes during the crisis revealed that Kennedy had also put the blockade in place, as an attempt to provoke Soviet-backed forces in Berlin as well.

Explanation:

In 1962, the American government was worried that the USSR would attack America from Cuba, because Cuba is near enough that the missiles could reach almost any city in America