By the beginning of this year, homegrown but foreign-led, foreign-funded AQI controlled most of the cities in Anbar and elsewhere; basically half the area of non-Kurdish Iraq, through a program of extreme violence and fear.
Don't take my word for it. There are only two things you have to read. I beg of you to take my little homework assignment and report back to the thread your thoughts.
Read the
National Intelligence Estimate for Iraq's Prospects for Security as excerpted by the New York Times.
And then read Michael Yon's
Bless the Beasts and Children.