The US never invaded Cuba though.

Well, not officially and certainly not effectively.

Umm… Bay of Pigs? Which is what led to the Cuban missile crisis, along with the installation of nuclear capable ballistic missiles in Turkey.

The US would have invaded Cuba during the Cuban missile crisis, if Khrushchev hadn’t backed down.

https://en.m.wikipedia.org/wiki/Monroe_Doctrine

Well, they tried. And botched it. And almost started an nuclear war over a sea blockade of Cuba back then.

But the US did put a blockade around Cuba. Any ships going to/from Cuba could be searched by the US.

Ukraine gave up its working russian-inherited nuclear warheads. So, no. This is not the same.

Putin is just another authoritarian ruler, a dictator. He will use any excuse he wants to invade; in this case he is using NATO membership and separatist movements.

Ukraine gave up their nukes almost 30 years ago.