The biggest and most powerful gang has been, for several centuries, a collection of like minded Sunni Moslem groups living in and around Baghdad. This great city was founded by the Arab conquerors of what was then called Mesopotamia. The city became a center of Islamic learning, and a major commercial power because of its location in the fertile Tigris-Euphrates river valley, and all those trade routes. But all that wealth attracted conquerors. The Mongols leveled the place in 1258, and trashed the place again in 1400. The Persians, who often controlled the region before the Islamic empire showed up, returned in 1524. The Ottoman Turks finally conquered the region 1638 and set about getting the area organized. The Turks were practical, and brutal. Putting troops inside the major cities took care of controlling the urban areas. But there were dozens of major tribes in the rural areas that were a major headache. The Turks made deals with the major tribes, often involving annual payments to the tribal chiefs, to keep the peace. This meant not raiding Turkish controlled territory, and sometimes policing the lesser tribes. Keep in mind that from the Mongol destruction of the area in 1258 until about 1850, the population of modern day Iraq fluctuated between a million and 1.3 million people. And about 40 percent were members of nomadic tribes. Most of the rest were farmers in the Tigris-Euphrates valley. There were over a hundred tribes. Most were Arab, but about twenty percent were Kurdish and a few percent Turks and remnants of other ancient peoples (like Assyrians, who were also Christians). Most of the Moslems belonged to the Shia sect, which was looked down on by the mainline Sunnis.
Most importantly, the Sunni Moslems were dominant in central Iraq, around Baghdad. This city was always the administrative center of the region. But until the 1920s, Iraq was ruled by three different Turkish governors. The north, Mosul province, was considered part of Turkey proper and was a majority Kurdish area, as was much of southeastern Turkey. Baghdad was run, for the Turks, by Sunni Moslem Arabs. Southern Iraq was run from Basra, and was dominated by Shia Arab tribes, but Sunni administrators.
The tribes always had lots of guns. When American troops began confiscating weapons in 2003, they found some rifles that were over a century old. When the Turkish empire collapsed in 1918, thousands of military rifles and pistols got into circulation. When the British ran the area during the 1920s, they armed some tribes who were helpful to them. By the end of the 20s, the country was run by a constitutional monarch, and the king was a Bedouin, born in Mecca and raised in Istanbul. Tribal power was respected, for the king, and his family (the Hashemites) had worked with powerful Arab tribes for centuries. But the king also introduced several new "tribes" to Iraq, tribes that would bring enormous suffering and death.
The new nation of Iraq needed an army, and this became a heavily armed and influential "tribe" controlled by Sunni Arabs. This was so because Sunni Arabs from Baghdad were better educated and formed a talent pool for administrators and military officers needed by the Turks to run the area. When Iraq was established, it was only natural that these experienced men be used to organize and staff the new armed forces. It didn't take the generals long to realize that they had a lot of political, as well as military, power. The 1930s saw numerous coups organized by generals. The king managed to stay out of the way, but it was obvious that Iraqi politics was getting more dangerous. After World War II, a new gang arose, Arab nationalists. Once more, this crew was dominated by Sunni Moslems. This was where the Baath Party came from. By the 1960s, the fighting was over, the king was dead, and the Baath Party proved to be the survivor. But this was only because Baath was more ruthless, violent and better organized. But in order to survive, Baath introduced still more gangs to Iraqi politics; mainly the secret police organizations. Learning from communist experience, Baath set up multiple security organizations, to keep an eye on the army, the national police, the tribes and each other.
Saddam Hussein was the architect of Baath and he terrorized and downplayed the traditional tribes. This changed when Iraq went to war with Iran in the 1980s and Saddam needed wider popular support to mobilize the country against the Iranians. He began doing what the Turks had done; rewarding the tribal leaders that supported him, and attacking those that didn't. While there are over 2,000 tribes and clans in Iraq, there are only about three dozen that really matter. Some of these, especially the major Kurdish groups, have over a million members. In the south, many of the Shia tribes are heavily influenced by Shia religious leaders. Saddam had depended on a few large Sunni tribes (including his own) as a base of support. You can still make deals with the tribes, as is being done now. But there are new tribes that present some unique problems. The Iraqi armed forces may have been dissolved, but the troops are still there. They are still a tribe. Same with the security organizations. The senior people in the army are all Baath. They have been excluded from public life. The army can be rebuilt as a professional (non-political) force. That won't be easy, but unless the army is run by people willing to accept civilian control of the military, you can expect a new Saddam to appear in short order. The former members of the security services will be a long term source of problems. Some will become part of criminal gangs, others will return to their tribe and make themselves useful. In the short terms, some of them will continue to fight. The Baath Party was a huge gang, with several hundred thousand full and part time members. While many have now returned to their tribes, a large number still think of themselves as Baath, and are willing to fight for the revival of Baath party power. This idea is easier to maintain in Sunni Moslem areas that received a lot benefits from Baath when Saddam was in power.
Most of the gangs in Iraq are looking out for their own interests. This makes it more difficult to build the nation of Iraq, but easier to keep the peace in what is known as Iraq.
The Gangs of Iraq; Iraq has always been a rough neighborhood. For thousands of years the area has been a collection of independent minded cities and tribes. We think of "Ancient Babylon" as a culture rich in achievements like laws, literacy and empires. That's all true. But because Iraq is situated on the easiest route (for armies, especially) from India and Central Asia to the Middle East, the area has never been very safe. Law and order is fine in theory, but as practiced in this part of the world, people long ago learned to supply their own law and order or die for want of security. Thus we have a country divided into hundreds of tribes, cities, religious and ethnic organizations. All armed, all ready to defend what's theirs to the death. These are the gangs of Iraq.