People unfamiliar with Kurds may not see the significance of the Kurdish army taking the Iraqi oil city of Kirkuk, a rich oil city they've long wanted as part of Iraqi Kurdistan.
To take Kirkuk, the Kurds had to come out from behind their semi-autonomous border (see: "A Success Story in the Middle East" for more about Iraqi Kurdistan) to annex a disputed part of Iraq. According to Reuters, the Kurds seized Kirkuk because the Iraqis had abandoned their posts and had left the city open to insurgents. The development also has wider and historic implications.
In the month Arahsamna the Medes went down to Arraphu [modern Kirkuk]... The Babylonian Chronicle.
In 615 BCE, the Kurds, the historic Medes, joined with the Babylonians (historic Iraq) to overthrow the Assyrians at Nineveh (Mosul), Assur, and Arraphu (Kirkuk). The Kurds, who feel their history deeply, consider Kirkuk as an ancestral city won at great cost which has the right of return.
Now, the Kurds have seized Kirkuk. Some might see their action as less than important given the rest of the mess in the rest of Iraq, but this is a sea change. Turkey and Iran (and Syria, if they resolve their own fracturing) have a significant stake in making sure the Iraqi Kurds stay in their mountains as a semi-autonomous region in Iraq to avoid civil war in their countries, and they have been vocal about it.
The longstanding fear by Iraq's neighbors has been that the Kurds would come for Kirkuk, for the oil and the history, which could result in the Turks, Syrians, Iraqis, and Iranians having to move against them to prevent their own large and dispossessed Kurdish populations from declaring independence and setting off a wider war.
The Kurdish Peshmerga, their army, is one of the most effective fighting forces in the Middle East. They've come out of their mountains which means they could enter the Iraqi-ISIS/Sunni fight, and, if they do, the terrifying ISIS insurgents will be facing a professional army.
Alternatively, the Kurds could be making deals with the Sunnis for the Kurdish part of Iraq plus Kirkuk or even to declare independence. Today, tellingly, the Kurds walked out of the parliament with the Sunnis which left the Shi'a government in Baghdad on its own.
Independence is a dream of every Kurd. The Iraqi Kurds have a territory that has been peaceful, tolerant, beautiful, democratic, and with significant capital investment from around the globe in shopping malls, universities, transportation hubs, industry and, of course, oil...
Disadvantaged Kurds in nearby countries (there are 40 millions worldwide) have watched the Iraqi Kurds and have waited for them to declare independence. Even if they don't, taking Kirkuk could cause countries like Turkey, with a long history of conflict with their Kurds, to think they might.
Another scenario in the realm of possibility could be a request from those outside governments, Turkey, Iran, Saudi Arabia, Jordan, for the Kurds to protect important parts of Iraq not yet taken by the ISIS (Islamic State in Iraq and Syria), a group so terrifying, al Qaeda denounced them.
Time and events that are moving fast will tell. The extent to which the U.S. will become involved (note: will, not might) will also move quickly and, if the current administration is true to form, involve partners. This will draw the world back to Iraq one way or another.
This is very a big deal.