Hoo boy. First, some context: Shiite militias, largely backed by Iran, are increasingly dominating Iraqi politics. The various militias are the armed wings of political parties, and are rivals of the Iraqi army and constitutional government for power. Excerpt:
So, now that we have learned a detachment of the 26th Marine Expeditionary Unit is deployed in northern Iraq, Asaib Ahl al-Haq, the League of the Righteous, has threatened to attack U.S. forces. The group was responsible for the kidnapping of British subject Peter Moore and also shot down a British helicopter in 2006. The league is commanded by an Iranian general. Hezbollah has also threatened U.S. troops in Iraq. Note that they subscribe to the widespread theory among Shiites that IS is in fact a U.S. creation, and the U.S. is only pretending to fight it. Even the largely reality-based Iranian news channel Al-Alam laces its report of the U.S. deployment with a dose of skepticism. That the U.S. secretly backs I.S. is also a commonplace of Syrian government-backed news sources.
The more than 50 Shiite militias in Iraq have between 60,000 and 140,000 fighters, according to estimates from the government and the Hashd itself. They are backed by tanks and weapons, and have their own intelligence agency, operations rooms and court of law.The larger militias, like Asaib Ahl al-Haq, the Hezbollah Brigades, Badr and the Peace Brigades, have been in place since soon after the 2003 ouster of Saddam Hussein. They are linked to political parties, effectively forming armed branches for politicians.
The situation is highly combustible, to say the least.