how did the himalayas affect the development of civilizations and regions?

Snowmelt from the Himalayan mountains produced the Indus and the Yangtze and Yellow have sources in the Tibetan ranges. China's and India's early civilization developed along these rivers. The Himalayas also kept the two civilizations fairly well separated until as late as the 2nd century when trade as a branch of the Silk Roads spread spices and Buddhism.

I would say the barrier was an asset. One of China's problems was there was little to stop the latest two-bit warlord from sweeping through and trashing the place. The Himalayas meant that at least they didn't have to worry about getting nailed from the southwest.