The ancient trade route from Kathmandu to Lhasa has existed for thousands of years. Nepal and Tibet have been friendly neighbours for the best part of history.
Now Tibet is part of China, but this hasn’t always been the case.
The British, in the early twentieth century, invaded Tibet on the pretext of protection from Russian influence. They forced a punitive treaty onto the Dalai Llama but it was virtually unenforcable. China was weakened at the time by constant invasions by Britain, France, Japan and others, and unable to enforce control in Lhasa, so Tibet was largely autonomous for a while.
Travels to Nepal 