Bonjour,
http://www.greatestcities.com/Asia/C...ache_city.html
Shache is in Xinjiang. The people in Xinjiang are considered as one of the minority tribes, so it's not in the middle of China. In Chinese history, China had had conflicts with many small countries in the border, and tried to make peace with them. China was such a big country and it had problem looking after itself. It's policy was to prevent other countries from attacking itself and to make peace. It didn't want to rule those small countries since they had their own language and kings and culture. For countries that were defeated in wars, as long as they paid tribute and sent gifts to China every year and acknowledged China was the big brother, China was at peace with them.
Btw, I've never heard of a version about going to Shache. The original Chinese text is 天竺， which most people agree to be India.