Only the US.
1945
1945 was the first year that a Nuclear bomb was successfully tested then used in combat.
US 1945
1945
1945
Since 1945.
While many countries have exploded test weapons, only the United States has ever used Nuclear weapons against an adversary. Two bombs were dropped on two cities in Japan Hiroshima and Nagasaki in 1945, to bring WWII to an end.
August 6, 1945: HiroshimaAugust 9, 1945: Nagasaki
From 1945 until the late 1970s or early 1980s the United States always had the most nuclear weapons. After then the USSR/Russia has had the most nuclear weapons.
There were tests of nuclear weapons but no other nuclear weapons were dropped on other nations as an act of war. Hiroshima and Nagasaki are the only uses of atomic weapons on other nations.
First nuclear explosion, the Trinity test shot.
The first ever nuclear explosion was a test in New Mexico in 1945