Question

Why did North Ireland, Egypt, Trans-Jordan, Syria, and Palestine fight on the side of the Allies

Answer 1

They were colonies of great Britain
Great Britain had taken over the areas and declared them to be British spheres of interests following the decline of the Ottoman empire. Egypt specifically was of prime significance to Britain as it was the new route to India and the colonies in the Eastern coast of Africa.

Answer 2

Northern Ireland, Egypt, Trans-Jordan, Syria and Palestine fight on the side of the Allies because they were colonies of Great Britain. They fought against the Axis Powers which comprised of a group of countries led by Nazi Germany and the Empire of Japan