Mostly for central and south america, it seems every time the communist boogeyman would rear its head the CIA would try and install the most brutal despot they could find as long as they swore to kill lots of communists.
Why not try and get these countries on e.g. US-aligned european-style social-democracies to draw them away from communist lure instead?
The wars and military operations to which you are referring were, for the most part, secondary to the larger 'conflict' which framed much of the later 20th Century known as The Cold War. (I'm sure you know this, just so we are on the same page). A significant European contingent of states were likewise party to military pacts arrayed against the Communist world and its satellites.
The US supported right-wing allies primarily as a counter-balance to Communist or 'leftist' expansion in areas they sought to influence, such as Central America. This was a block against the supposed domino theory which states that one successful change in ideology within a state can cascade through a region.
That being said, while many of these conflicts look similar in a macro sense they are all subtly different in a micro sense. Is there one instance which you are particularly interested in here? Then either myself or someone else could give you some more specific context!
For a good primer on Reagan-era activity in this sphere I would suggest:
T. Carothers: In the Name of Democracy - US Policy toward Latin America in the Reagan Years.
It provides a country-by-country background to US activity in promoting right-wing governments and undermining left-wing influence.
Edit: Text.