The result of all this has been, among other things, a resurgence of extremists within Iraq. Counting terrorists has always been a difficult endeavor. Nonetheless, estimates of their ranks were down to 1,000 or fewer as the United States departed in late 2011. That was off from a peak of 10,000 foreign fighters when violence was at its worst. Since U.S. combat troops left, however, AQI ranks have re-grown to at least 2,500 and probably higher. AQI is not the only organization to have concerns about either, as it works closely and is in some ways meshing with Al Nusrah in Syria as just one example.