President Barack Obama and his Russian counterpart Dmitry Medvedev sign a landmark treaty at the Prague Castle in Prague. The treaty commits their nations to major nuclear arms cuts. Under the new Strategic Arms Reduction Treaty (START), the former Cold War foes will be allowed a maximum of 1,550 deployed warheads, about 30 percent lower than a limit set in 2002. It also imposes limits on the air and submarine-borne intercontinental ballistic missiles that carry warheads.
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