Kirkuk is a Contested City and Province. The Iraqi Kurds claim that the city of Kirkuk has traditionally been a part of Kurdistan. The central government of Iraq says otherwise. Kirkuk is important because of its territory as well as oil revenue. Kirkuk is also the name of the province where the city of Kirkuk is located.
Kurdistan. The region referred to as Kurdistan encompasses territory in four different countries – Iraq, Turkey, Iran, and Syria. All four countries are wary of moves toward independence. The Turks have had a long-running conflict with elements of their Kurdish population. The Iranians have stamped out revolts by Kurds in their country over the past several decades. In Syria, the Syrian Democratic Front (SDF) is largely made up of Syrian Kurds and that organization has had huge success in taking territory over from the Islamic State fighters in Syria.
Kirkuk Province. The area of Kirkuk (province, governate, and other names have been used to describe the city and surrounding area) has traditionally been Kurdish with a mix of Arab, Turkman, and other ethnic groups as well. In the 1990s the Iraqi regime, under Saddam Hussein, conducted an “Arabization” of the city and province. After the 2003 invasion Kurds began moving back into the city.
Referendum for Independence. A recent vote was held on September 25th in Iraqi Kurdistan on whether the Kurds should push for independence. The vote was overwhelmingly (90%) in favor of Kurdish independence. It is important to note that the Kurds have not declared independence. The future plans of the Kurdish Regional Government (KRG) are uncertain. It could be they wanted to hold the referendum in an attempt to seek concessions from the Iraqi government (retaining possession of Kirkuk, the right to send oil to markets, government money for public services, and greater autonomy).
Fighting Breaks Out. At on Sunday, October 15, 2017 it was reported in several media outlets that the Iraqi Security Forces had advanced to positions in south Kirkuk held by Peshmerga forces. Fighting was reported in several locations on the outskirts of Kirkuk involving the use of artillery and tanks.
Regional Aspects. The regional implications of the Kurdish independence movement are significant. Iraq and none of the neighboring countries with a Kurdish population want an independent Kurdish nation on their borders. The possibilities of the independence movement spilling across the borders cannot be discounted. In addition, it upsets the fragile balance of power in the Middle East.
US History with the Kurds. The United States has a unique history with the Kurds of Iraq. Over the past several decades the United States has been engaged in several overt and covert relationships with the Kurdish people of Iraq.
1991 Relief Effort. Most Americans became aware of the Kurds when they saw the humanitarian crisis of the Kurdish people that fled the Iraqi army shortly after the end of the Persian Gulf War unfold on CNN. Days after the end of the Persian Gulf War the Kurds revolted (some say encouraged by the US). The Peshmerga enjoyed initial success but were quickly crushed by Iraqi helicopters and tanks. The Kurdish people, fearing a massacre, fled in the millions to the mountaintop borders of Iran and Turkey in the middle of winter. The United States led an international humanitarian effort called Operation Provide Comfort to relieve the suffering. A protective area and ‘no fly zone’ was set up and maintained until the invasion of Iraq took place in 2003.
OIF and the Kurds. During Operation Iraqi Freedom the Kurds were instrumental in seizing control of areas of northern Iraq. The 10th Special Forces Group linked up with the Peshmerga and tied down several Iraqi division in northern Iraq.
US Assists Kurds in Resisting ISIS. One of the major factors that pushed the U.S. into the current conflict with ISIS in the Middle East was the Islamic State offensive against the Kurds in 2014. Kirkuk, Irbil, and other cities were threatened. US air power and special forces advisors on the ground helped the Peshmerga halt the ISIS offensive in northern Iraq. At the time it seem to many observers that there was no organized resistance to ISIS in Iraq except the Kurds. The Iraqi army had folded and fled to the Baghdad and Shia areas of Iraq.
US Policy toward Kurd Independence and Future Support. The United States has publicly and officially dismissed the Kurds quest for independence. It maintains that an intact Iraq with the Kurdish, Shia, and Sunni areas remaining part of Iraq is the best solution for the peoples of Iraq and for the stability of the Middle East. While it doesn’t support the independence movement the United States (and other nations) have been deeply involved in assisting the Kurdish forces in the fight against the Islamic State fighters. Equipment, training, and advisors have worked closely with the Kurds since the summer of 2014. However, in light of the current situation – the possibility of a fight between the Kurds and the Iraqi Army – the US support of the Kurds may sharply and quickly diminish.
US Options. This conflict between the central government and the Kurds has put the United States in a difficult position. The US (and other Coalition partners) have special operations forces and conventional forces working along side the Iraqi Security Forces (ISF) as well as the Peshmerga. US airpower, ISR, and artillery support has provided significant assistance to the ISF. Perhaps these important assets can provide some leverage. Or do the Iranians simply step in and fill the void?
Possible Targets of Iraqi Military. The oilfields are an obvious target. The Iraqi government will attempt to control the oil fields, denying the oil revenue to the Kurds and using it for the central government. The K1 Air Base (Kaywan) located five miles northwest of Kirkuk is another important target. When the Iraqi Army fled the ISIS fighters it left the air base unoccupied and ISIS moved in.  The Peshmerga took the air base from ISIS and have held it for the past three years. It is likely that the civilian airport will be a target as well. The city proper? That remains to be seen.
ISF Units in the Fight. The elite Counter Terrorism Service (CTS) is reportedly spearheading the offensive and the Popular Mobilization Units (Shia) are operating in the area. In addition, elements of the 9th Division of the Iraqi army and the federal police forces have taken control of part of Kirkuk province. The Kurds have reinforced some areas of the province while moving out (ceding to the government troops) some areas to the south and west of Kirkuk city.
Taking the Eye off The Ball. Unfortunately, this conflict between the Iraqi government and the Kurds has escalated just as the Islamic State was on the ropes. A conflict over Kirkuk will reduce the attention to ISIS and allow it to slip away and reorganize – probably reverting back to being an insurgent / terrorist group once again. 
How Does this End? The Peshmerga has a long history of fighting prowness. They clearly halted the ISIS advance in late 2014 and early 2015 into Kurdish areas at a time when the Iraq army completely folded and fled the field of battle. However, the Kurds are not facing the inept Iraq army of 2014. Over the past two years it has become a professional fighting force (well, at least its special forces components that have borne the brunt of the fighting). In addition, the Kurds lack an Air Force, heavy artillery, and international support. Poised on the borders are the Iranians and the Turks – both have moved infantry, artillery, and tanks to the border areas. Add to these outside players the Shia Popular Mobilization Forces (PMF) that have significant Iranian support.
Kirkuk is Key. The prize is Kirkuk. The city of Kirkuk is a regional economic center, it has significant oil fields, a major airport, and the K1 Air Base. If the Iraqi government manages to take Kirkuk from the Kurds then the conflict could end there with no further incursion into Kurdish territory. It isn’t likely that the Kurds will give it up without a fight. The risk that the Iraqi government takes is the threat of a long-range insurgency by the Kurds that could take years to end.
Probable Outcome? The Iraqi Security Forces take the regional airport, K1 Air Base, the oil fields, and much of Kirkuk province. The city proper is retained by the Kurds. ISIS catches its breathe and regenerates. The staff at CENTCOM loses a lot of sleep. SF teams put their ‘Warrior – Diplomat’ skills into play.
 The Iraqi 12th Division of the Iraqi Army (over 12,000 soldiers) fled the air base in August 2015 during the northern Iraq offensive of the Islamic State (ISIS).
 A host of observers have predicted that ISIS will revert back to an insurgent / terrorist organization after all of its territory has been retaken. The Iraqi government still has a long counterinsurgency fight ahead and it can ill afford to lose the support of one of the more effective fighting formations in the country (Peshmerga).
References: The US Army in Kirkuk: Governance Operations on the Fault Lines of Iraqi Society, 2003-2009, by Peter W. Connors, Combat Studies Institute Press, Fort Leavenworth, Kansas, 2011.