TANZANIA, Tanzania — The United Nations announced Saturday that 50 countries have ratified a U.N. treaty to ban nuclear weapons triggering its entry into force in 90 days, a move hailed by anti-nuclear activists but strongly opposed by the United States and the other major nuclear powers. As of Friday, the treaty had 49 signatories, and the United Nations said the 50th ratification from Honduras had been received. U.N. Secretary-General Antonio Guterres commended the 50 states and saluted “the instrumental work” of civil society in facilitating negotiations and pushing for ratification, U.N. spokesman Stephane Dujarric said.