There were many ways in which Eisenhower's Cold War foreign policy was quite similar to Truman's. The so-called "Eisenhower doctrine," in which the United States pledged economic and other aid to nations resisting the spread of communism, was essentially applying the principle established by the Truman Doctrine (in Greece and Turkey) to the Middle East. Broadly, Eisenhower's administration pursued the same containment strategy that emerged under Truman. Still, Eisenhower's Cold War policy differed in key ways, which is why his administration described it as a "New Look" in foreign policy. Nuclear weapons technology had advanced greatly since Hiroshima and Nagasaki, and Eisenhower's administration used the nation's nuclear power as leverage against what they saw as implacable communist expansion. Eisenhower made it clear that he would use nuclear weapons against communist aggression in such locations as Taiwan. Known as "brinkmanship," this approach was used as a bargaining tool in negotiating a conclusion to the Korean conflict. Although he had expressed severe misgivings about the use of atomic bombs on Japan, Eisenhower saw nuclear weapons as a cheaper alternative to maintaining a large conventional force, an approach that led to an "arms race" with the Soviet Union. The President also used, to a far greater extent, covert operations to overthrow what were seen as dangerous (but also democratically elected) leftist regimes in Iran and Guatemala. Despite these aggressive measures, Eisenhower also sought, to a greater extent than Truman, a rapprochement in the Cold War, meeting with Nikita Khrushchev in a highly-publicized summit.