Seemingly taking advantage of the central government’s inability to stem the advance of radical Sunni Islamists on the capital, Baghdad, Iraq’s Kurds on Thursday took the ancient city of Kirkuk to which they have historically laid claim.

Kurdish officials said their forces had stepped in to protect Kirkuk after government troops fled in the face of an offensive by the Islamic State of Iraq and the Levant, a Sunni extremist group that claims affiliation with Al Qaeda but is not actually recognized by the international terrorist organization. They took Mosul, Iraq’s second largest city, situated to the northwest of Kirkuk, without much army resistance on Tuesday.

Kurdish peshmerga fighters subsequently moved into Kirkuk, which lies on the border of the Kurdistan Regional Government’s autonomous territory, and took over many northern positions that had been abandoned by the national army, authorities said.

Capturing Kirkuk and the huge oil reserves it commands is an economic boon to the Kurds but perhaps even more of an emotional victory.

The city’s Kurdish and Turkmen residents have long resisted Arab rule but a referendum to decide its fate was repeatedly delayed by a central government that featured the transfer of Kirkuk to Kurdish control would accelerate the process of Kurdish secession and prompt Iraq’s remaining Shia and Sunni Arabs to demand separate states of their own as well.

Iraq’s Kurds were able to build the institutions they needed for an independent state after Saddam Hussein’s defeat in the 1991 Gulf War when the United States enforced a no-fly zone over the north of the country. They now have a parliament, with two fiercely competitive major parties that have nevertheless been able to work together in a coalition, a well as separate intelligence and military services.

The Kurdish region is also increasingly independent economically. It has attracted foreign investments, especially from Turkey, and is able to export oil into that country over land — despite the objections of Prime Minister Nouri al-Maliki’s administration in Baghdad which insisted it alone had the right to export petroleum.