The history of Western "democracy" ( the U.S. in todays world ) spread throughout the world is a very complex and debated subject. Some think the U.S. used criminal methods many times to take over countries ( look up "economic hitman" ). Others think that socialism and communism need to be wiped out, so the U.S. inspires nations through various methods ( usually economic and militarily ) to join NATO and receive protection if the bad communists invade. The west had Russia surrounded and the Ukraine was the last straw. Just as if the U.S. was surrounded by hostile enemies, finally we would try to stop them.
Russia is barely bordered by NATO countries or even Westernized countries. It's bordered by Azerbaijan, Belarus, China, Estonia, Finland, Georgia, Kazakhstan, North Korea, Latvia, Lithuania, Mongolia, Norway, Poland, and Ukraine. Also the Arctic Ocean, Black Sea, Caspian Sea, Sea of Japan and some other waterways. Of those, only Estonia, Norway, Latvia and Poland are NATO members.
Russia's longest border (besides the Arctic Sea) is with Kazakhstan, followed by China, Mongolia and then Ukraine. Russia's land borders with non-NATO countries dwarf those of NATO countries. 12,577 miles altogether.
NATO members: 872 miles. Non-NATO members: 11,704 miles.
Putin's true agenda is to restore the USSR to what it was before parts of it disintegrated in the early 1990s. The countries that split off have very little interest in becoming absorbed and fear being the next Crimea, which Russia invaded and annexed in 2004.
If countries in Russia's neighborhood felt they had nothing to fear from Russia, they wouldn't be so eager to join NATO.