800 years ago, Rus-Ukraine was asking the West to assist against the invaders from the East. In 1240, the Golden Horde took Kyiv after 2 weeks of siege and promptly burned it. King Danylo retreated to the western part of the country, and was going to fight back, so he built the fortresses, and convinced the Pope to call for a crusade. But no one came, and he was left alone. So he had to negotiate with the Horde, and meet their demands: pay tribute, demilitarization by destroying the fortresses he built, and, finally, joined the Horde in a couple of fights against some of those who did not answer his call. It took 80 years to push the Horde back.
This story has been repeated a number of times. And now it is repeating again. Putin wants the same as Khan Batu wanted: Ukraine should demilitarize itself and refuse to join alliances like NATO, in order to become defenseless. And eventually, he wants Ukrainians in his army to move further towards Europe.
This is what Europeans have to understand: You won’t be safe if Ukraine falls. Because it would take just a generation to “cleanse” the most ethnically conscious Ukrainians and draft the remaining ones into the Russian army. Look at Chechens: They were fighting for their independence against Russia furiously in the nineties, but now many of them are now serving in the Russian army (even though many emigrated, and now are fighting on the Ukrainian side). Or you may look back at Ukrainians too: in 1919 they lost to the Red Army, and as part of the USSR, they invaded Afghanistan, Finland, Hungary, Czechoslovakia, and many other places. It took 72 years to set themselves free.
This is how it works: the nation that loses to Russia becomes “Russian” until it frees itself. Russia is like a cancer that spreads and never stops, and is hard to cure. Ukraine does not want to be part of Russia again. They paid in blood for centuries. And I am sure you do not want Ukraine to become “Russians” for another 70–80 years, and lose dozens of millions of people again as they did in the 20th century.
Ukraine just cannot avoid fighting. So they would prefer to fight as free people against Russia than to fight against other countries as part of Russia.