The inability (or simply slowness) of the government in stamping out these largely Sunni Arab terror groups has made the government very unpopular (although corruption and mismanagement help the hatred along). Shia Arabs are over 60 percent of the population but they are the victims of this terrorist violence over 80 percent of the time. As a result, police and army counter-terror units are arresting more and more Islamic terrorists. But until the Iraqi Sunni Arab community accepts democracy and Shia rule there will always be new recruits, sustained by Sunni Arab criminal gangs.
A year ago it became obvious that something had changed among the Sunni terrorists still operating in Iraq. Roadside bombs were still going off but they are smaller, poorly placed, and causing fewer casualties. Bombing operations in general were less sophisticated. This was largely the result of a much smaller al Qaeda movement and the conflict within the Iraqi Sunni nationalist movements (who want another Sunni dictator running the country.) While al Qaeda still considers Iraq a major battleground, al Qaeda does not have the resources it had seven years ago. Back then al Qaeda had over 30,000 active members, now it has less than 2,000. Back then Iraq was the major front for al Qaeda and over a hundred volunteers (most for suicide bomb missions) entered Iraq (usually from Syria) each month. Now only one or two volunteers come in each month and usually not via Syria. More al Qaeda members leave Iraq each month, to Syria mainly, as well as Yemen, Pakistan, Somalia, Africa, and other places where al Qaeda groups still survive.
There has been growing religious violence in Anbar, where local police can be bribed or intimidated into inaction, allowing Islamic radical and Sunni nationalist groups to maintain bases. The national government has not pushed the issue, with the violence level (about ten incidents a week) remaining steady for the last few years. Sunni leaders in Anbar accuse the national government of taking orders from Iran, to keep the violence going in Anbar, in order to punish the Sunni Arabs.
The Sunni Arabs are determined to regain control of the government. Their main tactic has always been to use terror attacks against Shia Iraqis and thus trigger a decisive battle that the Sunnis would somehow win. Western observers could never understand this, as it makes no sense. The Shia Iraqis, who now control the government and security forces, could crush the Sunni Arabs but the Sunnis do not believe this would ever happen. It's an article of faith that the Sunni Arabs must prevail. It is God's Will. Besides, most Sunni Arabs remember when (before 2003) they controlled, and received, most of the oil income. The other 80 percent of the population (Shia and Kurds) got scraps. The Sunni Arabs miss the good old days and want them back. This is something to kill and die for.