Russia has around 1,500 peacekeeping soldiers at the request of Transnistria for the last couple of decades to guard against an armed invasion by Moldova.
Right.....
The thing is, Russia interferes in countries of the former USSR. Look at Kazakhstan, they had protests, Russia went in and helped stop the protests. The Putin said that Kazakhstan should say in the "greater Russian world". He essentially told the Kazakhstanis that they're a Russian satellite state whether they like it or not.
Same for the Ukraine. Putin has been interfering there almost from the start of his presidency. Poisoning people he didn't like, promoting those he did like.
Transnistria is another part of the Soviet zone that Putin wants to make his own. He has troops there because it's convenient for him, it gives Russia power in the region. Maybe it is stopping Moldova taking Transnistria, the threat of war with Russia for a country the size of Moldova is even worse than for the Ukraine.
The fact that Putin is interfering in almost every country that was a part of the USSR, and the fact that he seems intent on taking the whole of the Ukraine for that very reason, and not because of the jumped up claims he's making.
If he doesn't want NATO on his borders, then taking the Ukraine is crazy, seeing how all of the Ukraine's neighbors, except Russia and Belarus, are either in NATO or have an individual partnership action plan in place. It would literally increase the NATO border for Russia.