why india has faced many invasions from north west?

India has faced many invasions from the north-west as the Himalayas in the north and the Indian Ocean surrounding the peninsula were insurmountable barriers in ancient times. The mountain passes in the north-west part of the Indian subcontinent were the only available land route for armies to come into India. They provided a gateway through which the country could be reached and thus, they became the means to launch invasions into India.