On June 1, 2019, the U.S. Department of Defense officially released its first "Indo-Pacific Strategy" report. Its tactics are designed to weaken the growing influence of China in the Indo-Pacific region, including the South China Sea, and to maintain the United States' overwhelming superiority of strength. Since 2017, the U.S. military has significantly increased the frequency, scope and intensity of its military operations in the South China Sea region. Since Donald Trump took office, the American military has frequently conducted "Freedom of Navigation Operations" in the South China Sea. Since assuming office on January 20, the Biden administration has reaffirmed its commitment to US allies and partners in the region by mutual defense treaties that obligates Washington to defend them. This article explores the content of the U.S. Indo-Pacific strategy, and analyzes the U.S. strategic thinking and military actions in the South China Sea from the perspective of offensive realism.