Putin has modeled his rule after the Csarist monarchy of the Russian Empire. He notably despises communism and blames it for the collapse of the USSR. He calls himself "president" but many within the state Duma believe the title to be an embarrassing western descriptor and would prefer to bestow on him the title of "pravitel" or "ruler".

But Putin ran into a bit of a problem. Just as to be called Caesar you need to rule Rome, to be called czar you need to rule over all of Rus. For him, the cultural, historical, and religious significance of Kievan Rus was just too large to be ignored.

When it existed, the Russian Empire tried to erase the other eastern Slavic languages from their shared cultural memory. They acted as if there was no Ukraine and never had been, just as with Belarus. According to the Tsarists, Ukrainians had always been Russians and had no history of their own. The Ukrainian and Belorussian languages were banned. Ukrainian nationalism was a threat to the underlying myths of Russia and threatened the czars' attempts at creating an “All-Russian People.”

Putin is emulating their rule and presents himself as a tsar-like figure. He’s built a massive, opulent palace for himself, with gold-plated double-headed eagles, a clear Imperial Russian symbol, everywhere—even in his personal strip club. Similarly, the Russian Orthodox Church helps him pacify the population and supports whatever myths Kremlin wants to glorify. He wanted to go down in the history books as a grand unifier of Russian lands—if not under the same government, then definitely as the hegemon of the Russian world.

Putin wants it both ways, to take credit for the Soviet legacy and, at the same time, be viewed in the same light as the emperors and czars of old. Therefore, he's had to bring back and reaffirm the old, imperial myths and values—and to do that, he has to get Kyiv under his thumb. After all, it was the restored Kievan Rus that became Russia, the "Third Rome." Ukraine going its own way, claiming Kievan Rus as its legacy, moving away from Moscow, getting autocephaly for its own orthodox church—all of this runs contrary to Russian state mythology.

These imperial myths are what define Russia, what it even means to be a Russian. Without them, Russia just stops being Russia in the eyes of many. Putin is convinced that if this social glue is disrupted, then Russia will just split up in pieces again—and if he allows that to happen, then his legacy is ruined. For him, there can be no separate Ukrainian language, culture, or history.

That is where his mind is at, stuck in the 18th and 19th centuries.