North Korea conducted its third nuclear test on February, 2013. Two nuclear test preceded this one, the first in 2006, and the second in 2009.

However, the nation that has performed the largest number of nuclear tests since 1945 is the United States, a total of 1,032. In the same period, the USSR/Russia performed a total of 715 nuclear tests, and France performed a total of 210 nuclear tests.

Source: Statista: North Korea Conducts Third Nuclear Test