To answer specifically the question of the difference between "East and West" of Ukraine, the timeframe should considered the creation of Ukraine as one of the most important point.
Note: Speaking of East and West might make things look like Ukraine is evenly separated. In reality, only few parts in Donbass and Crimea had been subjected to prefer Russia, and not all the time.
In 1991, USSR collasped. The process of collapsed included several steps, but it is important to note that an important point that interests us was that presidents of the Republics in USSR wanted independence. All of them. Even Eltsine, president of the Republic of Russia, had a dispute with Gorbatchev AND the militaries who tried to putsch against Gorbatchev. It is important to understand that, at some point and even if in various lands (Baltic countries, Caucasian ones, Ukraine) and for various reasons, nearly ALL people that rioted or manifest were against communism and in favour of Perestroika. President of the Republics that were parts of USSR, Eltsine of Russia as well as Kratchouk of Ukraine, wanted independence in 1991.
In Ukraine specifically, religious organisations played an important role in affirming Ukrainian nationalism and the opposition to communism, which would also meant for them liberty. Russian language was acknowledged as a language that should stay in Ukraine to speak between the different ethnic groups, but the majority of protests were done in Western Ukraine, especially in Lviv.
In the chain of events of 1991, it is important to note that contrary to what happened in Baltic or Caucasus countries, Ukraine was still waiting for a solution like the one Gorbatchev proposed with a federation replacing the Union of the Republics. But the failed Coup d'Etat had precipitated everything and Ukraine promulgated independence.
Contrary to Transnistria in Moldavia, there were no immediate war about the position of the Russian minority in the Republic of Ukraine. BUT borders of the Republic of Ukraine were determined by what the communists had decided when creating USSR, in 1922.
And, if you look at that, you see that the Soviet Socialist Republic (SSR) of Ukraine followed the pattern of the previous independent Popular Republic of Ukraine (PRU), that was promulgated by a council, the Rada, that wanted to take distances with Lenine's promulgation of Russian republic (because Lenine was unclear on his promises of giving autonomy to Ukraine). This Republic had following borders:
On this picture, you see that the litigious regions of 2014 (Crimea and Donbass) were not part of Ukraine.
When the Soviets conquerred Ukraine, they created the SSR of Ukraine, following similar borders. It is only between 1939 and 1954 that the litigious regions were added. Which, with the hindsights of 2023, could be considered as an historic mistake because for probably only administrative dispustes, they created the conditions for a more than 100 000 dead war...
So we have answered why there is a dispute between "East and West" of Ukraine today, which caused the dispute of 2014. Now, there are reasons for this dispute:
- Difference of language: Usually a difference that triggers conflict when people have other reasons for that
- Difference of religions (Catholic, "Ukrainian orthodox", vs "Russian orthdox"): A more common reason for violent opposition
- Holodomor and all the domination that Russians of the USSR exerted on Ukrainians: this is a very important reason
- Post independence Russian influence on Ukraine, that through the corruption of elites, triggers resentment: Russia wanted Ukrainian political men favorable to her, so she involved in Ukrainian political life and when these men (and women) revealed corrupted, Ukrainian accused Russia. This triggers resentment. Note that today's Ukraine political men are also corrupted
For all these reasons, Ukrainian and Russians had reasons to hate each other. In 2014, the conflict inside Ukraine and the Russian intervention fed this hate. Then in 2022, Russian attack fed even more.