While items like the Spanish-American war suggest empire-building HAS gone on for over 100 years; the real uptick in covert actions (as in the development of an insidious, Deep State apparatus) took hold with the passage of whatever Act led (in l947) to the N.S.A. That organization and its CIA affiliate in conjunction with Organized Crime and Big Money has assassinated both American and foreign leaders that did not do the bidding of its clients: a select sampling of the 1%.
In this interim, Project Paperclip's deliberate integration of Nazi Intelligence into covert U.S. military operations also shifted the climate to one of Absolute Power using all sorts of mind control, stealth, and immoral acts to obtain its (Ends Justify the Means, Might Makes Right) objectives.
The inception of the NSA, the following McCarthy era purge of any left-leaning intellectuals (added to a major scare that silenced Hollywood pretty much thereafter), and the assassinations of Martin, Bobby, and John (Kennedy)... led up to 911 and essential rule by this hidden consortium of empowered entities.
More currently, the deregulation of media allowed for a handful of broadcast corporations to purchase all major mass media. This, in turn, paved the way for all propaganda, all the time: the wet dream of the military industrial complex now morphed into mass media as a military-media-industrial complex.