The world's highest mountain range, the Himalayas lie to the north and northeast of India. Snow covers the mountains year-round. The extreme cold and height of these mountains made them difficult to cross. So, outsiders from the east rarely entered the Indian subcontinent. The Hindu Kush Mountains lie to the northwest of India. The climate in these mountains is more desertlike. The people of central Asia were already used to such dry and hot weather in their homelands. So, they used the passes in the Hindu Kush to cross over into India. Based on the passage, what roles did the Himalayas and the Hindu Kush Mountains play when it came to outsiders entering the Indian subcontinent?