For all his shortcomings in other areas, Richard Nixon made more progress in foreign affairs than any of the other Presidents mentioned. His secretary of state, Henry Kissinger, negotiated an end to American involvement in Vietnam and also restored relations with the Peoples Republic of China. Nixon in fact visited China, the first American president to do so. He also was instrumental in the SALT talks with the Soviet Union which led to a cooling of the tensions of the Cold War.
President Carter's foreign accomplishments are more problematic. On a positive note, he did negotiate the Camp David Accords between Israel and Egypt, resulting in a lasting peace between the two nations. However, he was unable to resolve the Iran hostage crisis which remained a shadow over his presidency.
Gerald Ford's brief time in office left him little time for foreign affairs, as the nation was plagued with rampant inflation. Aside from retaking the USS Mayaguez after it was taken by Khmer Rouge forces, and signing the Helsinki Accords which further aided detente with the Soviets, Mr. Ford had few diplomatic accomplishments.