As the Association of Southeast Asian Nations (ASEAN) marks its 50th anniversary, members are facing uncertainty over the changing shape of power in the region. Meeting in Manila, officials from the bloc's 10 members have tackled a code of conduct for the South China Sea and a response to North Korea's missile tests. The 24th ASEAN Regional Forum brought in top diplomats from 27 countries, including the United States, China and Russia, on the region's key security matters. But the broader issue facing the group is U.S.-China relations. The stage is shifting, and each ASEAN country is trying to find its place in the new geopolitical balance....