The Sunni Arab terrorism is giving rise to an increasing amount of similar actions by Shia Arab groups. The Shia Arabs, unlike the Sunni Arabs, are not trying to take over the government. Once elections are held next month, the Shia Arabs will be the largest block in parliament. What the Shia gunmen are looking for now is revenge. What outsiders often forget is that decades of terrorism and violence by Saddam was done most often by Sunni Arabs who did not hide their identities. The Shia took names, and some are not waiting for trials. They have lists, and are out looking for Sunni Arabs to kill. It is personal. And the police are not bothering much with these vigilantes.
There about 115,000 Iraqi security troops on duty. This includes police, troops and security forces that basically guard things like power plants and oil facilities. Journalists over there tend to concentrate on those incidents where Sunni Arab soldiers or police run away. But the majority of the Iraqi armed forces and police are doing their job. The jails are filling up with criminals again, and the Sunni Arab gangs in central Iraq often attack Iraqi police and soldiers, only to find that they are Kurds or Shia Arabs, who are eager to shoot right back. Even some of the Sunni Arab police fight, but that isn't news.
NATO has agreed to help Iraq train police commanders and army officers, but few NATO members will actually send trainers. Most Iraqis (the Kurds and Shia Arabs) believe that the violence in central Iraq is supported by Saddam Hussein's many friends. This in includes Iraq's Sunni Arab neighbors, and many European countries (Russia and France were major weapons suppliers to Saddam). So NATO's reluctance to help them makes sense. Conspiracy theories are popular in Iraq, the one about France and Russia wanting to put Saddam back in power has gained some traction.
Shia Moslems have long been persecuted by the majority Sunni. While the Kurds are Sunni, they are not very religious. At least most of them. A small minority of Kurds support Ansar al Islam, an Islamic radical group in league with al Qaeda, and supported by Iran. While Iran is mostly Shia, there are some in the Iranian government who support anyone who will help kill American soldiers. A principal belief of Iranian Islamic radicals is that the United States is the major enemy of Islam and must be destroyed, or at least weakened, by any means available. This attitude is a bit much for Iraqi Shia Arabs, who were never fond of the Iranian government anyway. Arabs are a minority in Iran, and even though these Iranian Arabs are Shia, they have suffered persecution from the majority, non-Arab, Iranians.
Iraqi Shia Arabs have lived in fear, and domination by Sunni Arabs or Iranians, for over a thousand years. Now it is their turn to rule, and they are not eager to let their chance slip away.