The Soviets and Russians have always used "fear of attack" as an excuse for expanding their empire. Russia has been attacked twice from the West in the past 225 years, while it has attacked its neighbors in eastern Europe and the Black Sea at least 25 times in the same period, which is why almost all European neighbors of Russia have clamored to get into NATO.
Ukraine has much more to fear from Russia than Russia has to fear from Ukraine.
There is a good reason Ukraine is putting up such a fierce defense, which was completely unexpected by the Russians.