that is for both sides!
Imagine that Mexico turn to Russia side, just like Venezuela and Cuba! Trying to joint the new Russia and friends defense pact... how would the USA respond?
Cuba is small, Venezuela was far enough and still was attacked... how about Mexico!, right to the USA border! Now Russia wants to place anti-missile system there, just like NATO was doing in eastern Europe and planned to do in Ukraine... The Cuba crisis was nukes, this one is anti-nukes missiles.
NATO was trying to surround Russia, Russia attack end doing worse, as Sweden and Finland join NATO... but Belaruss and Ukraine are totally under Russian influence and trying to change is enough to cause problems. Yes, all central and most South America is also under USA influence.
Not saying that is correct, but it is the reality! Changes on those countries must be done slowly and mostly via democracy and economics (both subject to external influence, sure, but not always, Chaves won in Venezuela in a clean way the first time at least) , not by military positions or pacts