This is factually inaccurate. Russia annexed Crimea after fomenting pro-Russian separatists in the Crimea. The government was not "overthrown" by the separatists before Russia's military backed annexation. Russia tried the same thing in two provinces on the eastern tip of Ukraine (in the Donbass region), bordering Russia. Those provinces have been fighting the pro-Russian forces since 2014. The only government in those provinces remained under Ukrainian control, holding against the Russian backed separatists until the actual Russian military rolled in. Those separatists never took either province and advanced further lest than half the geographical region westward.

Also, Ukraine has been growing increasingly successful economically and politically. That's why Putin invaded the country. The Russian authoritarian regime cannot allow an economically and politically successful FREE society rise on its doorstep. That's counter to Putin's entire world view with himself at its center. The issue also comes down to simple geo-political greed on the part of Putin and his oligarchs. The country has vast natural resources wealth which Russia needs. Aside from Ukraine being known as "Europe's bread basket" and it's huge coal resources, the country is also rich in iron ore, natural gas, manganese, uranium, salt, oil, graphite, sulfur, kaolin, titanium, nickel, magnesium, timber, and mercury.