system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why did Russia invade Ukraine?
gpt
Ukraine had a pro-Russian president Viktor Yanukovych who sparked massive protests when he turned down a deal that would have brought Ukraine closer to the EU in favor of closer ties with Russia.

After he fled the country, a new, more pro-Western government was elected that promptly signed that deal. Putin's regime, seeing Ukraine as a necessary buffer and viewing Ukraine not entering NATO and the EU as a vital national interest, launched a covert war of aggression in the East of the country (where there are lot's of Russian speakers and pro-Russian sentiment is higher) and engineering the annexation of Crimea. The goal was essentially to throw Ukraine into chaos and prevent it from being able to get its shit together and be able to join NATO or the EU. Putin has done this kind of thing in other places like Georgia and Moldova as well.