With U.S.-China tensions increasing on a number of fronts, the main issue that could spark a military conflict over the long term is still one that is fundamental to their relationship: Taiwan.

Chinese fighter jets have entered Taiwan’s air defense identification zone seven times in the last two weeks, prompting the island to scramble warplanes to warn them off. While the total number of Chinese incursions this year is still largely on pace with previous years, the outburst over the past few weeks is unusual and could augur a dramatic escalation if sustained.

The military maneuvering reflects the ever-present potential for war over an island that China’s Communist Party has threatened to take by force ever since the nationalist government of Chiang Kai-shek fled the mainland in 1949. For much of the time since, the possibility of U.S. intervention has helped maintain the status quo — even after the Carter administration switched formal diplomatic recognition to Beijing from Taipei in 1979.