Kirkuk: The city that highlights Iraq's war within a war
Over the last week, Iraqi Security Forces (ISF) have redeployed into the capital and oilfields of Iraq's Kirkuk province for the first time since the invasion by so-called Islamic State in 2014.
But the ISF did not liberate Kirkuk from the jihadist group: rather they forced their way past Kurdish Peshmerga checkpoints to re-enter the combustible ethnic melting pot of Kirkuk city and its environs, which has been garrisoned solely by the Kurds since 2014.
A number of Peshmerga and ISF troops were reportedly killed in short clashes on Monday.
The incident is a reminder that below the surface of the struggle against IS, there are also many "wars within the war", focused on post-IS control of territory within Iraq.
Though the ISF operation only began early Friday morning, Iraq-time, the struggle to control Kirkuk has spanned six decades.
Iraq's oil-rich province of Kirkuk has been the subject of contending claims by different ethnic groups for almost 60 years. It contains a blend of Kurds, Arabs, Turkmen and Assyrians, and successive Iraqi governments launched persecution and displacement campaigns against Kurds and Turkmen from the 1960s onwards.
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Kirkuk is also home to some of Iraq's oldest oilfields, resources that Britain used to sustain its war effort in World War Two. The province now produces just over 450,000 barrels per day of crude.
Kirkuk is positioned at the narrowest point of the Kurdistan Region of Iraq (KRI), astride the main road between the western part - controlled by the Kurdistan Democratic Party (KDP) of regional President Massoud Barzani - and the eastern part - under the Patriotic Union of Kurdistan (PUK) of the late Iraqi President Jalal Talabani and other parties.
This has led successive Iraqi governments to build up major military garrisons in Kirkuk in order to present a threat to the Kurds, placing Iraqi tanks only a short distance from the Kurdish capital of Irbil or the region's second city, Sulaimaniya.
When Saddam Hussein's regime fell after a US-led invasion in 2003, the Iraqi Kurds sought to prevent Kirkuk from ever again being used as launchpad for attacks on its region. Though the US-built Iraqi army was present in the province, the Kurds ensured it was not allowed to enter Kirkuk city.
The Kurds assumed more and more control as the Iraqi military weakened in the aftermath of US withdrawal from Iraq in 2011. After the IS assault, the Kurds took full control of Kirkuk's oilfields and have been operating them and selling around 90% of Kirkuk crude oil exports ever since.
Kirkuk has lived in a strange "grey zone" - not quite a part of federal Iraq, but not fully part of the KRI. For instance, the Kurdistan Region has provided frontline security for the province, which bordered areas infested with Islamic State militants, but Baghdad has paid the vast majority of civilian salaries, amounting to about $135m (£110m) per month.
The 25 September independence referendum held by the Kurds in areas under their control, including disputed Kirkuk, prompted Baghdad to change the post-2014 arrangement.
Officials from Baghdad, Iran, Turkey, the UN and the US-led coalition lobbied hard to have Kirkuk excluded from the referendum, or to have the referendum postponed in all areas.
The Kurdistan Region's refusal to agree to these terms seems to have kick-started planning for an ISF redeployment to Kirkuk.
Increased momentum in the anti-IS campaign was also a factor, with Iraqi forces clearing areas like Tal Afar and Hawija in less time and with fewer casualties than expected. The ISF is very confident at the moment, and its elite US-trained units - the Counter-Terrorism Service and the 9th Armoured Division - achieved rapid success in seizing Kirkuk city.
There was also a hidden factor in the rapid collapse of the Kurdish defence in Kirkuk, related to disagreements within the Kurdish factions over whether to resist the ISF or strike a deal with Prime Minister Haider al-Abadi. Speculation is rife that Iran, the US or both supported the return of ISF units to Kirkuk.
The PUK defenders of Kirkuk city and its military bases gave way to the ISF advance and are now negotiating with Baghdad over a shared "temporary joint administration" of Kirkuk. The KDP appears to have entirely withdrawn from Kirkuk province and even its vital oilfields.
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The future of Kirkuk province will now be negotiated between the PUK and Baghdad. It may include joint security forces and a PUK-Baghdad revenue-sharing deal.
Oil will probably keep flowing out of Kirkuk via the Kurdistan Region and Turkey for now. In the coming year, Iraq and Turkey may cut a new deal with the Kurds on shared oil export schemes. The longer-term back-up plan may be to export Kirkuk crude via Iraq's southern ports, Jordan and Iran.
The gravest uncertainty relates to the future of the Kurdistan Region. Relations between the KDP and PUK could sink to historic lows in the aftermath of the controversial events in Kirkuk. The political and economic viability of the region is in question if negotiations with Iraq and Turkey do not yield positive results.
For instance, lacking Kirkuk crude or Turkish backing, the economic situation in the region is now dire and humanitarian suffering could escalate, both for Kurds and for the million-plus internally displaced persons and refugees sheltering there.
The war against IS may also suffer: already in Dibis, one of the areas from which KDP Peshmerga withdrew, there has been a loss of control that seems to have allowed scores - some reports say hundreds - of security detainees to escape from jails, many of them IS militants.
Territorial control before 16 Oct 2017
Dr Michael Knights is the Lafer Fellow at the Washington Institute for Near East Policy. He has worked in all of Iraq's provinces, and spent time embedded with the Iraqi security forces. His recent report on post-battle stabilisation of Mosul is available via the Washington Institute website. Follow him on Twitter at @mikeknightsiraq