For decades, Vietnam has bought nearly all of its arms from Russia/USSR. However, the changing geopolitical landscape applies a tension to this, and Vietnam must at least consider other options.

Resolves to the next country that Vietnam buys at least new 50 MBTs from.

new= those specific vehicles not used by another country's military

I will add more options if anyone can make a compelling case; I think the current line up mostly accurately reflects the market.

For cases where the provenance of a tank is ambiguous, I am going from Wikipedia. The inclusion of the word 'new' is intended to exclude a lot of these cases (which I don't anticipate would arise anyway).