Many people think this way: in the beginning there was Kievan Rus, and then it slowly divided into Russia and Ukraine, and this division happened only recently. Putin’s propaganda argues that Ukraine should belong to him, that this is simply a rebellion in his vassal lands.
In fact, everything was different. The Rus are a NORTHERN people, they appeared near the Baltic Sea and lakes Ilmen and Ladoga. The gene pool of the Russians was influenced by the Vikings, Finns and Karelians. And Ukrainians are a relatively southern people, they appeared near the Black Sea. Between them there was a huge empty space (where Moscow and all of central Russia is now), in their gene pool there are Poles, Jews and possibly other southern peoples. A couple of centuries passed before these 2 peoples met. They were not yet full-fledged states, but they already had their own principalities. In the 9th century, the Novgorod prince Oleg the Prophet captured Kyiv and created Kievan Rus (i.e. it was not the original form, but an occupation). After 300 years, it collapsed again - due to the invasion of the Mongols, but in fact, at that time it was already in a state of crisis. The principalities of the period of feudal fragmentation reappeared. So you see? This was not some sacred proto-form, it was just a temporary state.
And only then, throughout its history, Ukraine continued to exist in a state of occupation by various countries: the Tatars, the Galician-Volyn principality, the Poles, and the Russian Empire. But she WAS.
Georgia and Armenia also existed almost throughout history under the occupation of Islamic regimes and the Ottoman Empire, but at the same time they still retained their originality. It’s the same with Ukraine.
The only problem is the names. For a long time, both Rus’ and Ukraine did not have specific names and were called differently. Basically, self-identification took place by cities, for example they were saying: “I am from glorious city Torzhok" or “I am son of lands of princes” or “I am good christian”.
Word Ukraine did exist already but wasn’t the only one for this land. It meant smth like “Corner / Borderland”.