The Shias of Iraq, for centuries under minority Sunni domination and decades of particular abuse under Saddam Hussein, are viewed with suspicion by the Sunni Arabs (and Sunni Kurds, who are not Arab but are Sunni Moslems--but the Kurds are more secure in their mountains):
The scale of the ongoing demonstrations reveals the widespread sense of alienation that Sunnis feel in the new Iraq. Prior to 2003, Sunnis rarely identified as members of a religious sect and instead called themselves Iraqi or Arab nationalists. It was the country's Shia population that claimed to be victims, on account of their persecution by Saddam Hussein.
Today, the roles are reversed. Shia Islamists consolidated power in Baghdad after the toppling of Saddam's regime, and some -- particularly those who were exiled during Baathist rule -- now view all Sunnis with suspicion. In turn, many Sunnis take issue with the new political system, which was largely shaped by Shia and Kurdish parties. Today, the Sunni population is mobilizing against the status quo and making sect-specific demands, such as the release of Sunni detainees, an end to the torture of Sunni suspects, and humane treatment of Sunni women in jails. Moreover, demonstrators are calling for the overthrow of the regime, using slogans made popular during the Arab Spring.
The Iraqi Sunni Arabs weren't less sectarian than Shia because the Sunni Arabs thought of themselves as "Iraqis." After all, they defined being "Iraqi" as being Sunni Arab. And the Baath party that Saddam ran was all about pan-Arab solidarity--which was useful to justify their minority rule. The system was organized around Sunni Arabs and benefited them--especially those from Saddam's home town of Tikrit. Shias were just useful bumpkins--especially when the Sunni Arabs needed soldiers to die in the long war against Iran from 1980 to 1988.
Today the Shias have reason enough to be suspicious of the Sunni Arabs. Al Qaeda is regaining strength and it can do so because the terrorists have help from the Sunni Arab community in Iraq. Yes, not all of it is enthusiastic. Some support the jihadis out of fear. Others just look the other way when they see jihadis. But some are very enthusiastic seeing the jihadis as a tool to regain power. The end result is that the jihadis can kill Shias and Sunni Arabs who work in the democratic Iraq. It is a fragile democracy, but it is a democracy.
So some Sunni Arabs are mobilizing against the status quo? No doubt. They liked the old status quo. Indeed, many Sunni Arabs don't even believe they are a minority. Heck, everyone they know is Sunni Arab, right? So of course some are calling for the overthrow of the government. Some truly believe the Sunni Arabs--by numbers if not by basic superiority--should run Iraq.
Iraq's Shias are not pure in this fight. But maybe they wouldn't need to be so harsh if we were still there with ground troops to help them find the jihadis and to provide reassurance to all that rule of law is the way the political game is played now.
But the Shias can remember recent history as well as ancient history, and will do what it takes to prevent the Sunni Arabs from ruling Iraq again. The Shias didn't just claim to be victims--they were victims. Now they aren't victims. They don't want to go back. The Kurds, who suffered from Sunni Arab brutality (gassing civilians), should be equally wary of the Sunni Arabs even if joining with them can check Shia numbers.
Our influence shouldn't just be focused on getting the Shias to accept a certain level of Sunni Arab complicity in al Qaeda terrorism without responding. We need to pressure the Sunni Arabs to fully carry out that Awakening and destroy al Qaeda in Iraq. And we need to pressure the Kurds into not believing they can be secure in a landlocked Kurdish region if they abandon commitment to a unified Iraq. Autonomy to some level is great, but they need a way out. Who do they trust more to provide that outlet? Iraqis, Iranians, or Turks? At least with Iraqis they have ample access to levers of power within the system. And being within the system restrains the Shias from using force (which might not work anyway, given Kurdish short-term advantages over the central government in military power deployable to fight for Kurdish regions).
This is why we should have stayed in Iraq. Iraqis may yet work this out without the system blowing up into sectarian warfare, and achieve a reasonable democracy. But we risk much after so much blood and treasure for the trivial political objective of being able to say we "responsibly ended" the war in Iraq.