Joshua Hammer at The New York Review of Books:
The hesitation in the drive toward Mosul also has much to do with Iraq’s fractious politics. The three main forces advancing toward the city—the Iraqi army, the peshmerga, and the coalition of independent Shiite militias, some backed by Iran—are in conflict about their parts in the coming liberation. Nechirvan Barzani, the Kurdistan Regional Government prime minister, announced last summer that the peshmerga would play a “central role” in the liberation of Mosul, which has a minority Kurdish population. The top commanders of the Iraqi security forces, dominated by Shiites, insist that the Kurds stick to the outskirts of the city, which is itself largely Sunni—then withdraw as soon as the battle is over.
The Shiite militias, poised within striking distance of Mosul in parts of neighboring Kirkuk province, have also demanded that they participate in the Mosul operation. “They played a huge role in the liberation of areas [around Baghdad] and they are highly motivated,” a US military officer in Baghdad told me. But the prospect of armed Shiites sweeping through Mosul has alarmed many Sunnis, who recall the killings of Sunni civilians during the liberation of Fallujah and other parts of Anbar province last spring. Some Shiite militia leaders, meanwhile, say they will oppose any attempt by the peshmerga to march into Mosul. Kurdish leaders are also demanding a referendum on their own independence as soon as the Islamic State is driven out of the country. Al-Abadi has hedged on Kurdish independence, which is opposed by most of the Shiite majority. (The US government has repeatedly said it supports a united Iraq.)