Yes, the U.S. would help defend the Taiwanese For decades the United States has maintained a policy of ambiguity regarding the Taiwan-China issue.
China contends that there is only one China and that includes Taiwan.
And from time to time China threatens to exercise its sovereignty over the island and its people. On the other hand, Taiwan claims it is a separate, independent nation and will defend itself against any effort by China to absorb it. The United States has walked both sides of the street. The question was phrased to include the use of U.S. military forces. That created quite a flap in Washington and tightened some already rigid jaws in Beijing.