For years, Asia watchers have debated whether China’s growing military power really represented a threat to stability in the Pacific. Some observers, including myself, worried that China’s strength could ultimately undermine norms of behavior and force smaller states to accommodate Chinese positions on territorial disputes. That China had not yet actually moved to unilaterally change borders, interfere with shipping on the high seas, or attack its neighbors made much of the discussion academic.

We now have proof of China’s intention to assert its territorial claims with military strength. This week, Beijing set up a new provincial-level city government to administer all its island claims in the South China Sea, as well as administer all the waters in the Sea, and “elected” a mayor for its insta-city of Sansha. The new governing council will represent approximately 1,100 Chinese residents of three island groups, all of which are claimed by multiple countries, including Taiwan, the Philippines, and Vietnam, in addition to China.

The real news, however, is that Beijing is also setting up a military garrison on Yongxing Island, which is also claimed by Vietnam. The garrison will serve “self-defense” purposes and carry out military operations, according to Chinese news reports. While it is unclear now how large the garrison will be, it is a game-changing political decision by Beijing. It essentially reveals Beijing’s plan for controlling disputed territory, which was the concern of those of us who feared what the growth of China’s military would mean for how nations acted in Asia. It makes power politics the reality, not just the possibility, in the South China Sea, and it forces smaller nations to decide if they can in any realistic way continue to oppose China’s claims. If accepted by other nations, this week’s moves will signal the beginning of true Chinese hegemony in Asia, and the creation of a new norm of regional politics based on might.

Beijing’s announcement should put enormous pressure on Washington. There are times for quiet diplomacy and behind-closed-doors talk, and there are times to clearly draw a line in the sand. This is not a casus belli, of course; but neither can it be overlooked, for one garrison can lead to another and then another. It may not happen this year or next, but if the Sansha garrison becomes an effective power, and is allowed to stand, then it will inexorably spread. Washington must make clear to Beijing that this course will result in some response from America, such as enhanced military aid to Southeast Asian nations, the end of military-to-military discussions between China and the U.S., or a refusal to ease export restrictions targeting China. If we do nothing, and hope it’s yet another boast from a “paper dragon,” we will wake up to a South China Sea that is de facto controlled by China. That may well lead to an environment in which we will find ourselves pulled into conflict between China and its neighbors, or one in which we pull up stakes due to the desire to avoid confrontation, and thereby announce the end of our influence in Asia.