What prevented the Communist Chinese from invading Taiwan and completely defeating the Nationalists?

Some of the factors that prevent China from invading Taiwan are that it is located in a strategic shipping route. The United States of America can quickly send a fleet if such an invasion took place. Taiwan is under the United States of America interest in the Pacific. This was seen when President Harry Truman sent a fleet to prevent the Chinese from invading what was left of Chiang Kai Shek’s forces. Today the U. S. is still on the alert and even the Chinese would not risk going to war if it would lead to involving the Americans.