CAIRO (AP) -- Working in secret, European diplomats drew up the borders that have defined the Middle East's nations for nearly a century - but now civil war, sectarian bloodshed and leadership failures threaten to rip that map apart.

In the decades since independence, Arab governments have held these constructs together, in part by imposing an autocratic hand, despite the sometimes combustible mix of peoples within their borders. But recent history - particularly the three years of Arab Spring turmoil, has unleashed old allegiances and hatreds that run deep and cross borders. The animosity between Shiites and Sunnis, the rival branches of Islam, may be deepest of all.

The unrest is redefining Syria, Iraq, Lebanon and Libya - nations born after the fall of the Ottoman Empire. Already quasi-states are forming.

For the al-Qaida breakaway group that overran parts of Iraq this week, the border between that country and Syria, where it is also fighting, may as well not even be there. The group, known as the Islamic State of Iraq and the Levant, wants to establish a Shariah-ruled mini-state bridging both countries, in effect uniting a Sunni heartland across the center of the Mideast.

Other potential de facto states are easy to see on the horizon. A Kurdish one in northern Iraq - and perhaps another in northeast Syria. A rump Syrian state based around Damascus, neighboring cities and the Mediterranean coast, the heartland of President Bashar Assad's minority Alawite sect. A Shiite-dominated Iraq truncated to Baghdad and points south.

Fawaz Gerges, a professor at the London School of Economics, sees an ongoing, violent process to reshape government systems that have been unable to address sectarian and ethnic differences and provide for their publics.

"The current order is in tatters," he said. "More and more and more people are coming to realize that the system as it is organized, as it is structured, is imploding."

The new frontiers, backed solely by force of arms, may never be formally recognized - it's not easy to actually create a new country - but given the weakness of central authority that may not make much of a difference.

The Islamic State's campaign is helped by Sunni discontent with Assad's Alawite-dominated Syrian government and the Shiite-led government in Iraq, two states whose borders were drawn by Britain and France after World War I.

The militants' capture of Iraq's cities of Mosul and Tikrit makes their dream of a new Islamic state look more realistic. It already controlled a swath of eastern Syria along the Euphrates River, with a spottier presence extending further west nearly to Aleppo, Syria's largest city. In Raqqa, the biggest city it holds in Syria, it imposes taxes, rebuilds bridges and enforces the law - its strict version of Shariah.

Historically, Raqqa and Mosul and the surrounding areas that make up Northern Mesopotamia - a region known as the Jazira - have had more in common with each other than they did with distant Southern Mesopotamia centered on Baghdad and Basra. The desert wadi routes that the Islamic State uses to smuggle its weapons, fighters and money back and forth across the border are the same trade routes established five millennia ago when the first cities arose in the Upper Tigris and Euphrates valleys.

And the Islamic State is not the only group with ambitions.

Iraq's Kurds, who run an autonomous region in northern Iraq, seized control of the city of Kirkuk, ostensibly to defend it from the militant group's advance. But they may not want to leave. The ethnically mixed city historically holds a revered status among Kurds and they claim it as their own. Holding it will only further stoke the longtime hopes among many Kurds of declaring outright independence.

Syria's Kurds, meanwhile, have taken advantage of the turmoil of that country's civil war - now in its fourth year - to take control of the pocket of northeast Syria where they predominate.

In North Africa, Libya is grappling with its own centripetal forces since the 2011 fall of Moammar Gadhafi. The authority of the central government in Tripoli has collapsed as multiple local militias take power in cities and regions around the country. In the eastern half of Libya - historically a distinct entity centered around Benghazi - there are calls for autonomy.