So a few things.

If the election weren't legitimate, why do Crimeans still stand by the decision they supposedly made at gunpoint to this day? Why don't they remember there being Russian soldiers being present during the referendum? Why would Ukrainian citizens be welcomed into Crimeans communities now if this had simply been a nationalist land grab? Why didn't Ukraine invest in Crimean infrastructure and social services between 1991 and 2014? Why would Russia invest in that same infrastructure and social services post 2014? Why weren't Russian citizens allowed to vote in the referendum, only Ukrainians with Crimean residency?

https://www.mintpressnews.com/return-russia-crimea-story-referendum-lives-since/262247

Comparing this situation to the relationship between the US and Iraq/Basra is grotesque and intellectually dishonest so there's no point in discussing that further.