(Interesting article exploring the success of insurgencies since the time of Bonaparte. Be sure to check out the graph.)
Two centuries ago, Napoleon Bonaparte sent his armies into Spain to overthrow a monarch who had once been a French ally. Napoleon, who believed he was touched by the hand of destiny, predicted his troops would be welcomed as liberators by ordinary Spaniards. He was wrong. The resulting Peninsular War from 1808 to 1814 seriously undermined French prestige, handed Napoleon a stinging defeat and produced a raft of unanticipated consequences that included the outbreak of deadly civil wars.
Historians would have a field day exploring parallels between Napoleon's Peninsular War and President Bush's war in Iraq, but that is not where we are going today. The Peninsular War interests us because it is one of the earliest examples of an asymmetrical war -- Spanish insurgents faced down the powerful French army by using stealth, deception and the support of civilians. It is the war that gave us the term "guerrilla."
Two political scientists recently examined 250 asymmetrical conflicts, starting with the Peninsular War. Although great powers are vastly more powerful today than in the 19th century, the analysis showed they have become far less likely to win asymmetrical wars.
More surprising, the analysis showed that the odds of a powerful nation winning an asymmetrical war decrease as that nation becomes more powerful....more...
http://www.washingtonpost.com/wp-dyn/content/article/2007/03/04/AR2007030401260.html