The reason for all of this is the US-arranged coup that resulted in a Ukrainian civil war, and the stated intention of Zelensky to join NATO.
Russia should have acted more forcefully after the coup, making it clear that risk of a NATO-Russia war was great and probable unless the US stopped its interference. Missile attacks on Ukrainian military facilities should have been undertaken, while its army was weak and disorganized.
During the Vietnam war, American planes mined Haiphong Harbor and killed Soviet sailor there. Goose-Gander algorithm applies here.
I’ll never understand why Putin spent so much time whining like a rejected schoolboy about US moves, which he should have known would be relentless if not stopped with force.
Placing a Russian military base in Venezuela would also have been productive, and remains a possibility.