The Atomic Energy Act (AEA) differs from federal environmental statutes in the extent to which it displaces state regulation of matters addressed by the federal government. Under the AEA, the federal government has the exclusive authority to regulate the construction and operation of nuclear power plants for radiation hazards. Congress first enacted legislation to provide for exclusive federal control of nuclear materials in 1946, shortly after the use of atomic weapons at Hiroshima and Nagasaki ended the Second World War. The utilities argued that the moratorium was motivated by safety concerns over the hazards posed by nuclear waste and therefore was preempted. Additionally, the utilities contended that the moratorium conflicted with the federal government's policy to continue licensing nuclear power plants in the absence of a waste disposal technology and also frustrated the federal goal of the promotion of nuclear power.