Ukraine and Grenada, Putin and Reagan?

Set on opposite sides of the world, Ukraine, with Crimea, and Grenada would seem to share few similarities. One is located in the temperate, even Arctic zone. The other is tropical. One is large, flat, and expansive. The other tiny and hilly. What these cases do share is the experience of superpower invasions for the safety of superpower citizens. Reagan invaded Grenada to save American students at its medical school (and pursued regime change too). Putin has moved to help fellow Russians in Crimea and perhaps too eastern Ukraine. Let's take them both at their word. The lesson: if you are a national leader and wish to avoid such invasions, don't allow in any citizens of superpowers.