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.

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 Muammar Gaddafi. 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 centred around Benghazi — there are calls for autonomy.

The contours and regimes of the Mideast are rooted in the 1916 Sykes-Picot accord, named after the two British and French diplomats, Mark Sykes and Francois Georges-Picot, who negotiated it in complete secrecy.

Under the deal, London and Paris carved up Ottoman Empire's Middle Eastern lands into spheres of influence. A series of later treaties after the end of World War I set the final boundaries, eventually creating Lebanon, Syria, Iraq, Jordan and a British mandate in Palestine that paved the way for the creation of Israel. The lines were drawn according to British and French interests with little regard to realities on the ground.

For example, mainly Sunni Mosul — along with Kurdish areas further north — was thrown together with Baghdad and the overwhelmingly Shiite south to form Iraq.

Syria was cobbled together from what had been the Ottoman provinces of Aleppo and Damascus, along with the long-separate coastal areas dominated by Alawites, an offshoot of Shia Islam.

Lebanon was broken away as a French-protected Christian protectorate, and Sunni and Shiite Muslim areas were added, creating a sectarian mix that has erupted into civil war and constant turmoil.

Cities like Acre, Haifa, Nazareth — which by administration, trade and clan were long connected to areas now in Lebanon and Syria — were instead looped into Mandate Palestine and now are in Israel.

Perhaps the most artificial creation was Jordan. But, ironically, for all its arbitrariness, Jordan looks at the moment like the most stable of the post-World War I creations.

Despite the foreign-drawn lines, the countries that resulted were relatively stable for the next century. In part, that's due to the grip of autocratic regimes. But also, people developed true identities as Jordanians, Iraqis, Lebanese or Syrians — even if at the same time they considered the borders illegitimate colonial creations.