We don't have any treaty obligations to fight for the Philippines claims on the Spratly islands. And, the 1887 boundary convention signed by France and China at the conclusion of the Sino-French war, recognizes China's ownership of the Spratlys. Japan wrested possession of the Spratlys from China in 1939. But they were returned in 1947 after Japan had surrendered and was in their restitution phase. North Vietnam also recognised China's ownership of the islands.