What affected the development of ancient India the most

The development of ancient India was most affected by its isolation and natural protection.

Explanation:

India gave rise one of the first civilizations in the world. Not just that, but this was a civilization that was highly advanced for its time and unlike the other civilizations of its time it doesn't seem to have had any military orientation or confrontation with other people groups. To put it simple, this civilization developed in relative safety and peace.

The fact that India has the biggest land natural barrier in the world protecting it and isolating it from the rest of Asia, meant that the people had little to fear when it came to invasions and conquests. Having such a huge burden off their minds, the people were able to focus on other more productive matters, so they managed to get involved and achieve great success in numerous scientific fields, managing to become a highly advanced civilization with relativey equality and peace among its citizens and rullers.