Another question which is fair to ask is why does the US insist that Ukraine joins Nato?
The main reason Russia will not allow Ukraine to join Nato is because if it joins Nato, the first thing the US will do is build permanent missile batteries with weapons pointed directly at Russia. As they did in Romania and Poland.
The second reason is that Russia has no natural borders. The big empire of the day, whether its the Mongols, Napoleon, the Ottomans, the Germans , the Brits, the Nazi's and now the Americans, tend to show up at the western border to relieve Russia of some land. They cannot allow a openly hostile military to set up shop in Ukraine. Which is what is happening now , hence the war talk.
The 3rd reason is that Ukraine is a Russophone country. Ukrainian is a Russian dialect. Just as the United Kingdom is made up of different sub groups, so is the Russian world. But to put a finer point on it, half of the country believes themselves to be Russian. The other half doesn't.
Kievan Rus' was a loose
federation of
East Slavic,
Baltic and
Finnic peoples in
Eastern and
Northern Europe from the late 9th to the mid-13th century,
[4][5] under the reign of the
Rurik dynasty, founded by the
Varangian prince
Rurik.
[5] The modern nations of
Belarus,
Russia, and
Ukraine all claim Kievan Rus' as their cultural ancestors.