The US has gotten a lot closer to Vietnam in terms of trade relations over the last 5 to 10 years. The US now regards Vietnam as a strategic interest to be aggressively developed.

The US will import about $50 billion worth of goods from Vietnam in 2017. That's up from $10 billion a decade ago.

That's equal to 25% of Vietnam's entire GDP.

It's also almost entirely one way, it's about as pure of a trade deficit as they get, so Vietnam is being doused with USD capital the same way China was in the early days of its growth boom. That's going to get a lot more dramatic yet, as the US wants some other large partners to work with in the region. For Vietnam's part, they seem perfectly happy to take the trade & capital inflow and put it to use rapidly expanding their economy.