Why didn’t post-WWI Middle East borders match ethnic or religious lines?

Answer: Because populations were already mixed, and postwar border-making was then dominated by outside powers

Because many ethnic and religious groups had long lived mixed together, making neat borders hard to draw — Wrong. Mixed populations made clean identity-based borders difficult, but that alone does not explain the final map.

Because outside powers dominated border-making after the war, prioritizing strategy and interests — Wrong. Great powers mattered, but they were drawing across an already mixed and overlapping social landscape.

Because populations were already mixed, and postwar border-making was then dominated by outside powers ✓ — Correct! The mismatch came from both forces together: populations were already mixed, and the final borders were heavily shaped by war, diplomacy, and great-power interests.