As we all know, enemies of the United States come and go and the longer they espouse revolution and/or communism and stand up to the United States, the longer they stay enemies! Currently, the U.S. does not recognize/have diplomatic relations with only three countries--two recreated by revolutions that the U.S. doesn't like--Iran and North Korea--and Bhutan, the kingdom that continues purposely to isolate itself having diplomatic relations with only India.
I'm on the way to visit a former U.S. enemy, but now recognized diplomatically by the U.S.--Cuba. This trip will be the third in 18 months and the second since the U.S. reopened diplomatic relations with Cuba. The Obama administration took the big leap of talking with the "enemy" with its secret discussions with the Cuban government over a period of two years. While the discussions were proceeding, commercial businessmen and journalists provided the political cover for Obama to withstand the withering criticism from those who strongly opposed dealing with the Cuba government that had been in power since the Cuban revolution in 1959. The U.S. broke diplomatic relations with the new Cuban government on January 3, 1961 because of its nationalization of U.S. businesses in Cuba and its alliance with the Soviet Union. On July 20, 2015 U.S.-Cuban relations were reestablished after 54 years. On March 20, 2016, President Barack Obama visited Cuba, becoming the first U.S. President in 88 years to visit the island.
Yet, despite diplomatic relations, U.S. sanctions and restrictions remain on trade and commerce with Cuba due to strong south Florida anti-Cuban government sentiments.
The U.S. and Cuban decisions to dialogue showed that long broken diplomatic ties can be reestablished. The Obama administration's negotiations with the Iranian government to suspend the Iranian nuclear program in 2015 has not yet led to reestablishment of diplomatic relations broken 38 years ago in 1979 after the Iranian revolution, seizure of the U.S. Embassy and holding 52 U.S. diplomats for 444 days. The U.S. will not talk about reestablishing diplomatic relations as it maintains that Iran is meddling in the affairs of its neighbors-Iraq, Syria and Yemen. Iran reminds the U.S. that the U.S. has invaded and occupied countries in its neighborhood for over 16 years-- in Afghanistan and Iraq, and has military operations in other countries in the region--Syria and Yemen.
Peoples Republic of China
In another part of the world, in July 1971, Secretary of State Henry Kissinger made a secret trip to the People's Republic of China (PRC), followed by President Richard Nixon's visit to China in 1972. The U.S. did not recognize its former enemy until 30 years after its founding as a communist state because of the PRC's participation in the Korean War on the side of the North Koreans. The U.S. switched recognition from Taiwan to the PRC on January 1, 1979 during the Carter administration, seven years after Nixon's visit.
Interestingly, from the creation of the communist Soviet Union in 1917 through the Cold War and after the dissolution of the Soviet Union and the 1992 establishment of the Russian Federation, the United States has never broken diplomatic relations with this "enemy." Even with the current high tensions with Russia, dialogue continues and cooperation in certain areas, for example the Russian launches and return of international astronaut corps to the International Space Station, has not been jeopardized.