Crimea has a strategic value to Russia its their largest warm water naval base, the rest of Ukraine is nothing but a liability. They can hold Crimea because it

Crimea has a strategic value to Russia its their largest warm water naval base, the rest of Ukraine is nothing but a liability. They can hold Crimea because it has a large Russian ethnic population and like it or not regardless of the reasons behind it a sufficiently significant portion of it seems to not to mind being under Russian control the same cannot be said for the rest of the country. The reason why Russia isn’t going to go much beyond Crimea is the same reason why Turkey never really tried to annex the Greek part of Cyprus it knew it cannot control it and it doesn’t want another Kurdish situation which this time would be also supported by another NATO member. There are a lot of reasons to why but none of them are really that complex. Russia’s movements in theater are the same since the early days of the Russian empire and are governed by geography the rest can be easily factored in by measuring environmental factors and Russia’s own capacity and capability. Syria as well isn’t that complicated, Russia didn’t want to lose an ally and their only port in the med and they as sure as hell didn’t want another NATO controlled zone in the region. Beyond that they also needed a “real” conflict to test the modernization of their military its the first time Russia has been employing combined arms with precision ground, naval and air based strikes in its operational history. Syria was a great excercise for them they got to test all their new toys on targets that the general public doesn’t really care about whilst Ukraine and previously Georgia had many more limitations due to geopolitical pressure.