"Military theorists from Sun Tzu to Clausewitz have warned of the dangers and unique challenges of combat in and around cities. By 2030, 60 percent of the world’s population is expected to live in massive urban areas or megacities. These megacities feature slums and endemic homelessness, uncontrolled expansion/urban sprawl, and lack of basic support structures making operations complex and extremely dangerous. Urban terrain is a powerful advantage for entrenched combatants. It magnifies the power of defense, and diminishes an adversary’s advantages in technology, firepower and mobility." -- Commander Arthur M. Castiglia, Jr., USAWC Strategy Research Report, 2015.