The Vietnamese are enemies with all their neighbors. They invaded Cambodia after the Kymer Rouge crossed the border to murder Vietnamese towns. They are also rivals of the Thais but they would ally themselves to take over Laos and Cambodia --"inferior" peoples-- and split the spoils.

This tiny nation has won every battle they've fought, against the US and even against China--once they repulsed a Chinese invasion. Now, they need allies and really want the Americans to protect them from the Chinese. For their part, The Americans want a military base in Asia, so they have become allies. No hard feelings, I guess.

People seem really psyched now in VietNam. After generations of foreign occupation, first by the Chinese, then the French, then the Japanese, and then the Americans, they are finally in peacetime and can focus on getting rich.