The prisoner's dilemma demonstrates how decisions that are individually rational can create worse outcomes collectively. The incentives for the individual {prisoner,nation} are not compatible with larger group dynamics.

The solution is to create an environment where individual decision makers are strongly incentivized to make decisions that are collectively beneficial. This is where modern telecommunication technology and - in spite of it's problems - economic globalization can help a lot: nobody wants to drop bombs (atomic or conventional) on another country if their friends or business partners live there.

How do Russia's actions in Crimea fit into this model? In fact, I'd argue they invaded exactly because they had close close economic ties to the area. This is kind of what I'm referring to -- the rest of Europe wants to avoid war and Russia takes advantage by making aggressive military moves.

> they invaded

How many bombs did Russia drop on Crimea during that invasion?

Russia may have had ties to local areas like Crimea, but the are not as integrated economically and socially on a global scale. Compared to e.g. US/EU relations, a lot of people in the US still see Russia as suspicious/hostile.

Russia's attempts to disguise their initial presence with astroturf "popular support" is an example of the country being increasingly aware of how they appear on the international stage. Bombs become less appealing as the economic cost of pissing off the rest of the world grows. Unfortunately, there is still a lot of work to do to create that goal.