Dmitry Medvedev made yet another statement denying Ukraine's sovereignty and claiming it was "always part of Russia". Apart from providing a convenient mental shortcut to justify desperate Russian occupation of parts of Ukraine, this actually only testifies to the untrustworthy and deceptive character of Russian state politics, because Russian Federation has voluntarily signed and ratified a number of bilateral agreements with the same Ukraine, guaranteeing its borders and its sovereignty. If Kremlin can reject any formal agreement based simply on the fact that "it was once in Russian Empire", then how can anyone trust Russia on any other promises, informal or written? Not in this speech, but also frequently voiced by Russian officials is the argument that "Ukraine only exists since 1991" - as a reminder, Russian Federation also only exists since that year. So you really have to clearly declare which frame of reference you choose for comparison, because if you want to look at the cultural heritage, then Ukraine predates Muscovia by around 500 years.