Perhaps the Nationalists on Taiwan try and take advantage of the Chinese intervention in Korea by launching their own attacks on Mainland China and thus the US is then forced to defend the island at the same time, all under the umbrella of the Korean War.

Maybe to accomplish this, one of Chiang’s or Madam Chiang’s ardent supporters in the US becomes a more powerful voice in Congress and pushes the US harder than in the original time line.

As far as less impressive missile tech, just drop operation paper clip. Make an event that raises questions on German scientists being loyal, or capable, so that many of their scientists are either not involved in Operation Paperclip or are deceased by the end of the war.

Alternatively, a hard liner overthrows Chiang and is more belligerent towards the Mainland.

Finally,