This is a huge question to answer, almost too big for a single reddit post. I am going to respond with just the parts of it that I have studied in order to illustrate the complexity of the region.

Ukraine exists at a unique geographic location. It is crossed by a number of large river systems such as the Dnieper. It is at the crossroads of the Eastern European Plain and the Pontic-Caspian Steppe. It lies on the Black Sea. These factors have influenced the groups that have come and gone through the area throughout history, including Germanic groups like the Goths, Iranian groups like the Scythians, Turkic groups like the Khazars and Tatars, Greeks along the Black Sea Coast, Magyars (Hungarians), and various Slavic tribes, among others. From my background, I focus on the area in two distinct empires: The Khazar Khaganate, and the Polish-Lithuanian Commonwealth.

The Khazar Khaganate (7th century to 11th century) was a large Turkic empire which at its maximum extent exerted influence from the Aral Sea in the East to around the Dnieper River in the west and the edges of the vast forests to the north. The Khazars are notable for having Jewish rulers for a few centuries, with a few surviving primary sources in Hebrew. The Khazars effectively utilized their geographic position to dominate trade along not only the Volga River, but also around the river systems further to the west. Several Slavic tribes in modern day Ukraine and Russia paid tribute to them, along with Turkic and Finno-Ugric groups. I read a very interesting article by Dariusz Adamczyk entitled "Arab Silver Redistribution Networks in the Early Medieval Eastern Europe: Polycentric Connections and Entangled Hierarchies" which highlights the interconnected nature of these Khazar trading networks. Adamczyk highlights in his article how Khazar trading networks connected tributary groups such as the Slavs of modern day Ukraine to merchants such as Scandinavians, Arabs, Jews, and Hungarians, as well as the tribal rulers of areas like Poland who participated in this network in order to secure Arab silver currency. I won't go into the specifics of the article beyond that, but it does a very good job at detailing the dynamism of trade and movement in the area, connecting numerous groups from not just Eastern Europe and Central Asia but also Northern and Central Europe.

As Khazar power disappeared from modern day Ukraine, it was replaced by the other Turkic groups in the south and by the Kievan Rus' in the north. The ruling dynasty of the Rus' were known as the Rurikids, and they were among the Northern Europeans who had established a power base in modern day Russia during the period of the Khazar Khaganate. It was under the Rurikids that the Rus' converted to Orthodox Christianity, the dominant religion in Ukraine, Russia, and Belarus to this day. The initial seat of the Orthodox Church in the region was in Kyiv, but when much of Rus' was conquered by the Mongols the city began to lose its primacy and Orthodox power was transferred elsewhere, eventually ending up in Moscow by the 16th century. Much of the steppes of what is now Ukraine was still populated by Turkic groups after the Mongol Conquest, particularly centered around Crimea. Many of these Turkic Tatars converted to Islam.

By the 15th century, much of modern day Belarus and Ukraine were now part of the Grand Duchy of Lithuania, which had expanded into the area following military victories over Mongol successor groups such as the Golden Horde. Poland and Lithuania entered into a personal union in the late 14th century after the Queen of Poland married the Grand Duke of Lithuania. The 1569 Union of Lublin created a real union out of these two realms, the Polish-Lithuanian Commonwealth. The period of the Commonwealth saw the rise of what is called today the Ukrainian Greek Catholic Church, a denomination of Christianity in communion with the Catholic Church which nonetheless kept many doctrines and styles from Orthodoxy. The nobility of what was then-called Ruthenia integrated into Polish-Lithuanian society, becoming Polonized over time. The Jewish population in the area greatly expanded due to the relative religious tolerance of the Commonwealth.

In the south there were various Cossack groups, most notable the Zaporozhian Cossacks. These Cossacks challenged Polish rule of the region, and were fairly cosmopolitan in terms of ethnic and religious diversity. The Zaporozhian Cossacks eventually allied themselves with Russia, and brought what is now Eastern Ukraine into the Russian Empire. The Islamic Crimean Khanate was conquered by Russia in the 1780s, simultaneously with Russia's participation in the partitioning of Poland. As a result of the partitions, most of what is now Ukraine ended up as part of the Russian Empire, except for the region of Galicia which was taken by Austria. Galicia was a culturally mixed area, with a sizeable Polish majority in the west and a Polish minority in the east along with a major Jewish population.

I am going to cut this off here because I am less well acquainted with Ukrainian history during the period of the Russian Empire and the topic becomes even more complicated once you get to events like the Holocaust, but I think this does a decent job at highlighting the historic diversity of Ukraine. The region of Ukraine by the 1700s was inhabited by Slavic and Christian groups including Poles and Ruthenians, Islamic Turkic Tatars, Jews, and cosmopolitan Cossacks, among others. This isn't to say that Ukraine has an identical cultural dynamic like the settler-colonial United States, but it has historically had a large amount of cultural, religious, and ethnic diversity.

Sources and further reading:

The Jews of Khazaria by Kevin Alan Brookes

“The Political Economy of the Arab Silver Redistribution Networks in Viking Age Eastern and Central Europe: Polycentric Connections or Entangled Hierarchies?,” by Dariusz Adamczyk

God's Playground: A History of Poland Volumes 1 and 2 by Norman Davies