Demographics is key for any country's future.
Maintaining a growing population gives you an edge.
At its most basic level, population growth increases the whole size of the economy, including labour demand. The economy expands to meet the increased demand as more people buy goods and services. Politicians welcome population expansion because it allows them to talk about economic and job growth. Large corporations like population growth because it allows them to extend their client base without having to compete aggressively. Unions may benefit from population growth by expanding the total size of the labour force and hence their pool of potential members.
If we compare Vietnam to its Chinese and Thai neighbours we can see that Vietnam has a clear edge.
If we want to have an overview of the future, we should look at fertility rates in these countries. Once again, Vietnam is in a much better position than its neighbours.