The Himalayan mountains isolate India from the rest of Asia. This mountain range has some of the highest peaks in the whole world, including Mount Everest. The Himalayan mountains also make it hard for other countries to invade India, or for India to invade others.
China is the only country that could possibly invade India because they refuse to recognize that Bhutan has claims to the land near the Siliguri Corridor of India. The Himalayan mountains are the only reason India count protect itseld if China ever decided to invade. Other than that, having the mountains helped them protect others from the British during the colonial era because no one could effectively get around them.