Taiwan is the first island chain that includes the Japanese and Okinawan islands to the north and the Philippines to the south. Japan maintained sovereignty over Taiwan for fifty years, until Japan's surrender in 1945, at which point according to the terms of the Cairo and Potsdam agreements Taiwan was returned to China. When the San Francisco Peace Treaty was signed in 1951, however, Japan renounced sovereignty to Taiwan without stating whether the People's Republic of China (PRC) should assume sovereignty. The key PRC military advantage over the Nationalist defenders proved to be the large size of the People's Liberation Army (PLA), with the Communist junks and troops moving only at night. Both Communist and Nationalist forces fiercely defended their positions on numerous offshore islands, in the hopes of changing the strategic balance. Beijing's and Taipei's opposing territorial claims make the PRC-ROC situation one of the most complex of any of the ongoing maritime and territorial disputes between neighbors.