The collapse of the Republic, its causes and aftermaths, its moral dimensions, is a source of endless debate around here and always will be.
Having read Holland's two books (Rubicon, Persian Fire), one gets the sense he has an axe to grind against current events, and tries to link history as much as possible to current events. Even Holland admits later in the preface that comparisons between America and Rome are a cliche - but he has no problem milking the cliche (Pompei's campaign against the pirates is entitled "The War on Terror", for instance). So regardless of the issues surrounding the fall of the Republic, realize that Holland may have a deeper agenda.