In 1990, after years of legal and political action, the USA issued a formal apology and promised to compensate the families of Navajo miners who had died young of lung cancer through mining uranium ore for atomic bombs. The government in the 1950s confirmed that the cancers among miners were caused by exposure in the mines to high levels of radon produced by the decay of radium in uranium ores. Not until the late 1960s did it warn the miners of excessive levels of radiation in the mines and the dangers. It justified its silence on the basis of national security and its need for the uranium. In 1991-92, Congress appropriated $200-million to provide compensation to people injured or killed by the nuclear-weapons industry.