Which three regions were part of the Indian Ocean trade route?

Southeast Asia, India, Arabia, and East Africa.

The three regions that were part of the trade routes of the Indian Ocean were East Africa, the Indian Subcontinent and Southeast Asia.

The commercial routes of the Indian Ocean were controlled mainly by the Portuguese, who established trading posts along the African, Indian and Southeast Asian coasts. But the main colonizer of the area was the British Empire, which established a large colony in India.

The Dutch and the French also colonized the area, but on a smaller scale.