LONDON By expanding their arsenals once again, the nuclear powers are forgetting "lessons of the past," Spain’s prime minister warned Saturday, calling this a "historical error." Speaking at the Munich Security Conference, Pedro Sanchez expressed concern over nuclear rearmament and called on nuclear powers to sign a new START treaty after the last one expired on Feb. 5, leaving the US and Russia’s strategic arsenals with no binding restraints. "The world is becoming more unstable, and we