Harry S. Truman campaigned on European security, and in his inaugural addressed stressed the point: America had to be involved in Europe’s defense, not just its reconstruction. The Europeans agreed: their previously-formed mutual defense organization was focused more on Germany and excluded the U.S.; but the members quickly saw the bigger threat was to the east, and they would need American help in containing it.

On this day, July 21, in 1949  the U.S. Senate in a vote of 82 to 13 approved the North American Treaty, paving the way for North American Treaty Organization.

From its inception, the treaty’s mutual self-defense clause invoked only once, and not against the Soviet Union. When the United States was attacked on September 11, 2001, NATO organized a defensive response code-named Operation Eagle Assist. From October 4 until May of the following year NATO reconnaissance AWACS aircraft flown by 13 different nations made 360 operational sorties in the skies over U.S.  — nearly 4300 total hours of flying time.