So much so that it's actually the expectation!

Country wants to expand its territory? Most likely place to extend to is those in its borders. It's literally the lowest hanging fruit.

Small country being invaded by large country? Who are they most likely to turn to? Does it seem that unlikely that they'd go to the biggest actor who doesn't like that country? The enemy of my enemy?

Coincidence? I think not! It's literally the most logical thing