By Matthias Williams KYIV (Reuters) – Volodymyr Zelenskiy swept to power three years ago promising to end a war with Moscow-backed separatists in eastern Ukraine. He now faces a Russian invasion that could result in the overthrow of his government and the end of Ukrainian democracy. As Russia rained missiles down on Ukrainian cities including Kyiv on Thursday, Zelenskiy appealed to all citizens to defend Ukraine, saying weapons would be given to all who wanted them. “Russia treacherously attacked our state this morning, as Nazi Germany did during World War Two, ” Zelenskiy told Ukrainians in a…