One of the changes that marked the decline of the Roman empire was their increased reliance on mercenaries instead of citizen soldiers. Many were in it solely for the money (or salt) and not patriotism. The same was increasingly true of the wealthy elite. Sound familiar?
The essential problem with armed overthrows is that they rarely win the peace. Victory in the battlefield doesn't create sustainable institutions for a civil society. Pop quiz: when did World War 2 end? The fighting may have stopped in 1945 but the real answer is somewhere in 1947-8, when the Marshall Plan and the Occupation in Japan helped restore normalcy and gave the Japanese and Germans back control. That's why they are such strong allies today. That's why Iraq is not.