As a member of NATO, the U.S. agrees to help defend any member country that is attacked by a non-member country. During the Cold War, the primary threat to NATO was perceived to be the former Soviet Union. Accordingly, in order to make its commitment to NATO credible, rather than station all its troops in relatively safe areas, the U.S. chose to station many of its troops close to the borders of Soviet-friendly countries. How does this make the U.S. commitment to NATO credible?