When cavalry and artillery were gaining popularity in early modern Europe, Machiavelli in his Art of War continued to emphasize the importance of infantry, which was regarded as comparatively worthless. Nobody believed that foot soldiers, who we now refer to as "boots on the ground," could withstand the charge of cavalry. This was thought impossible until the mountaineers of Switzerland proved everyone wrong.
Once again, we are witnessing the remarkable ability of foot soldiers - "insurgents" - to withstand shock and awe campaigns carried out through aerial assaults. This feat is only underscored by the history of America's "Green Zone" in Iraq - a highly fortified fortress of steel and concrete - which has proven to be an embarrasingly weak outpost of security. If our army generals were actually trained in the art of war, they would know that the best fortress is built out of people, not out of steel.
One needs to look no further than Hezbollah to see the military folly of relying on heavy artillery to win battles against skilled foot soldiers. As Sabrina Tavernise writes in this excellent analysis of Hezbollah's roots in the people of Lebanon,
They cover medical bills, offer health insurance, pay school fees and make seed money available for small businesses. They are invisible but omnipresent, providing essential services that the Lebanese government through years of war was incapable of offering. Their work engenders a deep loyalty among Shiites, who for years were the country's underclass and whose sense of pride and identity are closely intertwined with Hezbollah. Their presence in southern Lebanon is so widespread that any Israeli military advance will do little to extricate the group, which is as much a part of society as its Shiite faith. "The trees in the south say, 'We are Hezbollah.' The stones say, 'We are Hezbollah,' " said Issam Jouhair, a car mechanic. "If the people cannot talk, the stones will say it."
Hezbollah is the people. If there is no better fortress than the people, the battle for Baghdad has long been lost.