A major step forward in the abolition of nuclear weapons: the elimination of the last U.S. mega-nuke, the B53 nuclear aerial bomb. This old Cold War bomb, which carried nine megatons of nuclear explosive and was approximately 750 times more powerful than the Hiroshima and Nagasaki bombs, was unusable in today's world with its tremendous non-discriminating overkill potential. One B53 could wipe out millions of innocent civilians and whole geographic regions (for example, the greater Los Angeles area), in a few seconds. Now it's time to take further steps by eliminating the thousands of reserve nuclear weapons in the U.S. and Russian nuclear arsenals, and to remove all tactical nuclear weapons from Europe. Until both nuclear superpowers get serious -- far beyond last December's New START agreement to reduce deployed strategic nuclear weapons to 1,550 on each side -- about reducing their expensive, dangerous, and unnecessary nuclear stockpiles, we'll continue to face the proliferation of these weapons of mass destruction to other countries such as Iran, North Korea, and more.