What affected the development of ancient india the most

Ancient India's development was mostly due to natural protection and relative isolation from the the rest of Asia.

Explanation:

There were four civilizations in the Old World that are considered as the cradles of civilization in this part of the world, those being Mesopotamia, Ancient Egypt, Hindus Valley Civilization, and Ancient China. All of the are civilizations that flourished along the banks of large rivers with frtile valleys. The Hindus Valley Civilization in India, was different than the rest though.

The civilization that developed in Ancient India was one that didn't engaged in military action nor there is any evidence of internal conflicts. Even later in history when the Aryans migrated to the region there was no military conflict but mixing of people and culture. The reason that this civilization managed to flourish and develop at a very high level for its time was the safety. The Himalayas are a natural barrier that prevented any military conquests from other parts of Asia, so the people were able to live without fear and in peace, being able to fully focus on science, phylosophy, and development of their society.