The modern map of the heartland of the Middle East was largely designed by British and French diplomats and strategists (namely Mark Sykes of Britain and Georges Picot of France) during World War I.
The Entente powers defeated the Central powers, the latter comprising first and foremost Germany but also, importantly for the future of the Middle East, the Ottoman empire, which ostensibly controlled the Levant — what today comprises most of what we know as Syria, Jordan, Israel, Palestine and Iraq. The Entente victory essentially allowed for the implementation of Sykes-Picot. It divided the heartland of the Middle East into spheres of influence between the two powers after what they assumed would be victory.