Cuba is your example? Really? Where Kennedy was ready to start WWIII when Russia placed missiles there? Let's note that Kyiv is closer to Russia than Cuba is the US, and missile flight time from Ukraine to Moscow is shorter than missile flight time from Cuba to Washington DC. Your example proves my point 100%

Tolerate? We invaded Cuba at least once. The US funded and armed the Bay of Pigs invasion. We tried at least 600 times to assassinate Castro.

"Semi-hostile"? Mexico has never been "semi-hostile" to the US.

The correct comparison would be to if Mexico or Canada said they were going to join the Warsaw Pact in 1975. No fucking way in the real world would the US have accepted that.