“their control and protection was covered by treaty agreements at the fall of the Soviet Union”
Yes, the same treaties which guaranteed the national sovereignty and territorial integrity of the Ukraine, which Russia subsequently violated multiple times.
One might say the US-orchestrated Maidan Coup of 2014, also violated Ukraine “ sovereignty” and it incited a civil war of resistance and then cultural genocide by ultra nationalist security services and special military units against Russian speakers in Crimea, Eastern and Southern Ukraine