Final answer:
The modern borders of the Middle East are the result of changes in global geopolitics, nationalism, and the eventual breakdown of the European mandate system, which diverged from the boundaries set by European powers after World War I.
Step-by-step explanation:
The current borders of the Middle East differ from those agreed upon by European powers after World War I because of various geopolitical developments and shifts in power dynamics throughout the 20th century. Initially, the Sykes-Picot Agreement in 1916 between Britain and France divided the Middle East without considering the ethnic and religious compositions of its diverse populations.
Nationalism and the pursuit of self-determination led to resistance against European-imposed boundaries. Adding to the complexity, the British government's Balfour Declaration, which supported the establishment of a Jewish homeland in Palestine, conflicted with both their promises to Arab leaders and the desires of the Arab majority.
Moreover, the mandate system implemented by the British and French ultimately did not ensure full European control, and over time, the affected nations forged their own paths toward independence, creating the borders we see today.