CAMP DAVID, Md.—The U.S., Japan and South Korea took a significant step on Friday toward creating a bulwark against common threats from China and North Korea, forging a sturdier three-way alliance to bolster security. President Biden hosted South Korean President Yoon Suk Yeol and Japanese Prime Minister Fumio Kishida at Camp David, in the first visit by foreign leaders to the presidential retreat since 2015. The three committed to consulting on threats to each’s security, working together on ballistic-missile defense, conducting annual joint military exercises and holding yearly summits to maintain the momentum. The stronger alliance forms part of a...