(CNN) -- President Barack Obama said Tuesday night in his State of the Union address that the United States will "lead" the international effort to curb nuclear proliferation -- saying North Korea and its "provocations" will "only further isolate them" and that Iran's leaders "must recognize that now is the time for a diplomatic solution." He also vowed to work with Russia to further reduce nuclear arsenals and to help make sure that nuclear arms don't "fall into the wrong hands."