Not long ago, China asserted its claims on the South China Sea by building and fortifying artificial islands in waters also claimed by Vietnam, the Philippines and Malaysia. Its strategy is to reinforce those outposts by swarming the disputed waters with vessels, effectively defying the other countries to expel them.The goal is to accomplish by overwhelming presence what it has been unable to do through diplomacy or international law.“China pretty clearly thinks that if it uses enough coercion and pressure over a long enough period of time, it will squeeze the Southeast Asians out,” said Greg Poling, director of the Asia Maritime Transparency Initiative at the Center for Strategic and International Studies in Washington.China’s actions reflect the country’s growing confidence under its leader, Xi Jinping. They could test the Biden administration as well as Beijing’s neighbours in the South China Sea, who are increasingly dependent on China’s strong economy and supply of COVID-19 vaccines.The latest incident has unfolded in recent weeks around Whitsun Reef, a boomerang-shaped feature that emerges above water only at low tide. At one point in March, 220 Chinese ships were reported to be anchored around the reef, prompting protests from Vietnam and the Philippines, which both have claims there, and from the United States.Philippine Defense Secretary Delfin Lorenzana called their presence “a clear provocation.” Vietnam’s foreign ministry accused China of violating the country’s sovereignty and demanded that the ships leave.By this past week, some had left but many remained, according to satellite photographs taken by Maxar Technologies, a company based in Colorado. Others moved to another reef only a few miles away, while a new swarm of 45 Chinese ships was spotted 100 miles northeast at another island controlled by the Philippines, Thitu, according to the satellite photos and Philippine officials.The buildup has inflamed tensions in a region that, along with Taiwan, threatens to become another flashpoint in the intensifying confrontation between China and the United States.Although the United States has not taken a position on disputes in the South China Sea, it has criticized China’s aggressive tactics there. For years, the United States has sent Navy warships on routine patrols to challenge China’s asserted right to restrict any military activity there — three times since President Joe Biden took office in January.