“The modern history of the Crimean oil and gas industry began in 1960, when the first onshore gas field – Zadornenske – was discovered.”
https://www.naftogaz.com/en/history-of-the-industry
In real life things can be very complex and neither totally just or totally unjust.
I am a frequent blog contributor and not a Ukrainian history professor. I’m pretty sure one will write a book.
Since we’re talking about modern history, in modern times Russia ceded sovereignty and borders of Crimea in 1994. It made sense at the time because otherwise the Ukes could have used those nuke fissionable materials & made a lot of bad, bad nuke bombs with them.
In 2012, more oil & gas was discovered and shortly thereafter, Ras Putin invaded the region in a straightforward conquest because he detected weakness [turns out he was correct] on the part of the concurrent American administration and Europe to do anything about his obvious tyrannical land grab. Then there was a not-so-weak-kneed prez, no activity from Ras Putin. Then there was another weak-kneed prez so Putin invaded again.