After holding out against unification demands from China’s communist rulers for more than 70 years, Taiwan is now at the heart of the deepening discord between China and the United States. The island’s fate has the potential to reshape the regional order and even to ignite a military conflagration — intentional or not.

“There’s very little insulation left on the wiring in the relationship,” Danny Russel, a former assistant secretary of state, said, “and it’s not hard to imagine getting some crossed wires and that starting a fire.”

China’s military might has, for the first time, made a conquest of Taiwan conceivable, perhaps even tempting. The United States wants to thwart any invasion but has watched its military dominance in Asia steadily erode. Taiwan’s own military preparedness has withered, even as its people become increasingly resistant to unification…

China now acts with increasing confidence, in part because many officials, including Mr. Xi, hold the view that American power has faltered. The United States’ failures with the Covid-19 pandemic and its political upheavals have reinforced such views.

Some advisers and former officers in China argue that the United States no longer has the will to send forces if a war were to break out over Taiwan. Under the right conditions, others suggest, the People’s Liberation Army could prevail if it did.