For most of the past five decades, an informal boundary ran down the center of the Taiwan Strait. Neither side formally acknowledged its existence. Neither side inscribed it in any treaty or agreement. Both sides, for most of the period between the 1950s and 2020, generally respected it: Taiwanese and Chinese military aircraft and naval vessels operated on their respective sides, and crossings were infrequent enough to be noteworthy events that required diplomatic management. The median line was a fiction that worked because both sides found it useful. China has now decided it no longer finds it useful, and the consequences of its erasure are visible in daily military operations across the strait.

The legal status of the Taiwan Strait has become an active diplomatic flashpoint rather than a settled background condition. The United States and its allies assert that the strait is an international waterway subject to the freedom of navigation that applies to straits used for international navigation. China asserts that the strait is Chinese internal waters, through which foreign military vessels do not have an automatic right of transit. These positions are irreconcilable, and the competition to establish which one is treated as authoritative by state behavior is a current, active dimension of the Taiwan Strait competition that operates below the threshold of military confrontation.

The Chinese aircraft carrier Liaoning sailed through the Taiwan Strait on Monday, April 20, according to Taiwan’s defence ministry — marking the first passage of a carrier through the waterway since late last year.

The transit is a deliberate signal. The strait, roughly 180 kilometers wide at its narrowest, is one of the most politically loaded stretches of water in the world. Beijing claims it as internal waters; Washington and Taipei reject that framing and maintain freedom-of-navigation as a standing principle. Sending a carrier through it is not a routine patrol — it is a message, timed and calculated.