Taiwan is also stategically important because it guards access from the Pacific to China and back. To the north there is Japan and South Korea (US allies), and

Taiwan is also stategically important because it guards access from the Pacific to China and back. To the north there is Japan and South Korea (US allies), and to the south there are Vietnam and the Philippines, who already feel the pressure of the expansion of China's influence (Chinese military bases in the South China sea), and are thus likely to side with the US in the future. Right now, China is sorta contained, but if the CCP can reassert itself on Taiwan, the situation will flip and the CCP will have full control about access to the mainland from the sea, and can freely access the Pacific.