It is the oldest trick in warfare that one side lulls the other side into complacency of winning an easy victory, then undertakes rear guard sniping action to inflict the equivalent of death by a thousand micro-cuts. The reason this strategy of war is still used is because it works so well. Equally effective is the strategy of guerilla warfare. Victory need not be secured by multi-billion dollar defense budgets. Victory is secured by sheer damage to infrastructure, supply lines, and convoys. In the era of high tech weapons, those things can be obtained with a small amount of Symtex and a remote control transmitting device. The Spanish railway bombing that killed 200 people effectively cost the terrorists a briefcase, some explosives, and a cell phone. It did not cost them their lives.
Guerilla warfare reached the Middle East during the first world war as proven by the activities of the Camel Corps that damaged and eventually destroyed Turkish rule. In a region where memory is long, the tactics that worked so well then remain part of the methods of war. Insurgents and irregulars played a substantial role in every successful coup, war, and other radical Islamic efforts in the region. Whereas the ancient armies of the sultans fought organized campaigns, now disorganized - or at least loosely organized - campaigns are the standard.
If military victories were based on might making right, many wars would reach very different results. Britain would still control the US; Germany might still control most of Europe; Napoleon would have preserved control of Egypt and Russia; the Roman Empire would have endured much longer than it did.