“We are now entering into a period of great power rivalry. The outcome is unclear, but it is critical that we stabilize the system.” That was the warning on Thursday from Singapore’s Heng Swee Keat, the man set to be the city-state’s next prime minister. China’s rapid ascent over the past decade, he said, has caused a clear shift in global politics, and those changes need to be addressed. The Singaporean deputy prime minister’s sentiment was echoed by other political figures and experts gathered in Tokyo for a conference on the future of the region. At the event, which was...