Many experts are now speculating that the Islamic State group is experiencing its death knell. It is losing territory, its finances are being drained and the number of foreign fighters recruited has reportedly dropped by as much as 90 percent from a high of 2,000 a month in the past year. Each week, the U.S.-led coalition's campaign to eliminate high-value targets seems to be achieving more of its objectives. In addition, substantial numbers of its fighters are defecting, especially from Syria.

Yet the recent reversals might only force IS to adapt its campaign of irregular warfare as other militant groups, including al-Qaida, have done. With foreign fighters unable to reach the battlefield, for example, IS leaders could instruct would-be jihadists to remain home and launch attacks there.

This would not bode well for predictions of the group's demise. Research shows that the median length of an insurgency is 10 years — and the greater the number of foreign nations involved, the more likely the insurgency will continue. The fight against IS, according to historic trends, is only in its infancy.