For example it states that Kievan Rus was Russian predecesor state, "in what is now Ukraine".
It's like saying Roman Empire was a French predecessor state in what is now Italy. Not the whole story.
Not that it matters much, but it's one of the constantly repeated points of Russian propaganda - that Ukraine is a temporary state with no history.
And considering the defense as explanation for military conquests of Russia - which country in the west was supposed to invade Russia through Ukraine? Eastern EU and NATO members, with no power to do that by themselves, no nuclear detterent, much smaller military budgets, and no territorial demands in Russia?
I propose different explanation: Russia is governed by Putin for over a decade, he promised "prosperity instead of freedom", and delivered till 2013, mostly thanks to high oil prices. Ukraine was always portraited by Russia as "almost Russia", and Ukrainians started revolutions to win "freedom and prosperity" through eventual accession to EU.
Putin couldn't allow that to success, because if that is possible in Ukraine - it's possible in Russia. Few years ago there were big demonstrations against Putin in Moscow and St. Petersburg after another flawed elections (famous 140+% of votes in some districts :) ).
As long as Ukraine is an enemy, and is in crisis - no risk of Russians doing Majdan in Moscow.