As a Harvard professor, he argued against Dwight Eisenhower's and John Foster Dulles's policy of rollback, saying that antagonism would push Eastern Europe further toward the Soviets. The Polish protests followed by the Polish October and the Hungarian Revolution in 1956 lent some support to Brzezinski's idea that the Eastern Europeans could gradually counter Soviet domination. In 1957, he visited Poland for the first time since he left as a child, and his visit reaffirmed his judgement that splits within the Eastern bloc were profound. He developed his ideas he called "peaceful engagement." Brzezinski became a naturalized American citizen in 1958.