"You have to understand that hierarchy in order to understand Iraq," Kean said. It explains, Kean says, why Sunnis will sometimes fight other Sunnis when conflict arises between families, clans or tribes. These groups all take precedence over the religious unity.
This hierarchy, however, does not always hold true. Many people identify themselves as Iraqis before their religion or province.
"I grew up in Iraq," said Zainab Salbi, the founder and president of Women for Women International. "But no one I know has a clan or tribe -- it happens in villages where Saddam came from and marginalized provinces. I would say yes, there are tribal areas in Iraq, absolutely. Is everyone like that? Absolutely not."
To give the mire of the Iraq conflict a sense of perspective, Kean compares it to four major historical conflicts -- but all happening at the same time and within one country.
For example, Kean says, the Iraq war is like trying to reconstruct post-World War II Germany while simultaneously trying to put down an insurgency (similar to those revolutions in el Salvador, Algeria and Vietnam), which wants to overthrow the government.
In addition, there are the warring factions between the Shiites and Sunnis -- a situation similar to what the United States faces in Bosnia when stopping Serbs and the Bosnian Herzegovina from fighting each other.
Finally, there are terrorist groups -- similar perhaps to the Irish Republican Army in Ireland. Most countries have dealt with each of these problems individually, but this gives you an idea of the scale of the problem in Iraq and the difficulty in untangling the mess of conflicting interests and groups.
The insurgency is the name for the group or groups who rebel against the current form of government in Iraq. The insurgency comprises the former members of Saddam Hussein's regime, such as the special Republican guard and militia, Kean says.
These people, those most involved in the violence under Hussein, were predominately Kurds and Shiites and became the initial foot soldiers in the insurgency. They were later joined by anti-American Sunnis who believed they would be disenfranchised by the new Shiite government.
With the many conflicting loyalties in Iraq, "power is fragile and split between a lot of different groups," retired Maj. Gen. William Nash said.
"Nobody is used to the government's way of doing business," Nash said. "Democracy is new and unusual, and the government is cobbled together. It was not won by a great margin, so to govern is very difficult. … That's why [Prime Minister] Maliki has so much trouble making things happen -- because he doesn't have that much power. And he doesn't have a monopoly on force [referring to the terrorist and militant groups]. And there are no security forces [police or military] at his disposal."
The power structure can be broken down into four different groups, ABC News consultant Fawaz Gerges says.