The United States became the only country to have used nuclear weapons in warfare when they dropped atomic bombs on Japan during World War II.
At the order of President Harry S. Truman during the final stage of World War II , the United States dropped nuclear weapons on the Japanese cities of Hiroshima and Nagasaki on August 6 and 9 , 1945 , respectively . United States . The United States emerged from as a global superpower , the first country to develop nuclear weapons , the only country to use them in warfare , and a permanent member of the United Nations Security Council .