You are aware that Russia already invaded in 2014?
No they didn't. They were already there. The biggest feature of Crimea is the naval base that Russia had been leasing since Ukraine had a legitimately elected government. When the US supported Nazi led coup regime took power they tried to cancel the lease. The Russians simply stayed put. They didn't invade. They were already there.
Are there any more fundamental understandings of recent history you would like me to catch you up on?