So if thousands of troops were already there - then why is NATO upset and talking about "invasion?"
Russia has leased bases in the Crimea. The Russian troops just rolled off them and invaded the rest of the Crimea. The bases were never under threat and are leased until the 2040’s. This is a simple power grab by Putin. Crimea is pretty big in Russian national mythology and Putin was PO’d that his stooge was booted from Kiev.