Kiev had no intentions of holding a referendum in prior to Russia invading. The Crimean peninsula is ethnically Russian. Russia invaded with the intent of allowing Crimea to hold a referendum. Had Russia not been there in Crimea Kiev could have moved in its army and blocked succession (if the results were the same).

That is a way to give some legitimacy to Russian actions. I personally don't believe any referendum/vote taking place immediately following a invasion is legitimate. The Kremlin way of looking at it would be if they hadn't invaded Crimea would never have had the chance to vote.

The Kremlin before all this accused the CIA of organizing the protests in 2013 and eventually the revolution in 2014 that led to the overthrow of President Viktor Yanukovych and his government. Yanukovych had been distancing Ukraine from the west and making closer economic ties to Russia. The protests were very much focused the Ukraine-European Union Association Agreement which Yanukovych suspended. This agreement gave Ukrainian citizens many of the rights EU citizens had including fair working rights and free travel visas to its citizens throughout the EU. As such it was a very popular bill and the President suspending it in favor of closer ties to Russia was what kicked off the uprising.

On 4 February 2014, the Presidium of the Supreme Council (Russia) considered holding a referendum on the Crimean peninsula's status, and asked the Russian government to guarantee the vote Now the reason all that is important is because the revolution started on February 18. Russia sees that whatever the outcome in Kiev it probably won't be positive to them. Russia invades Crimea on 20th. EU mediators signed an agreement the very next day reinstating the Ukrainian constitution. The referendum was held the next month placing Crimea in Russian hands. Obviously the west doesn't recognize the referendum.

If you look back at it