After World War Two and at the height of the Chinese Civil war in 1946 a British and American sponsored uprising sucessfully pushed Chinese troops out of Tibet. Many nations immediately recognised the Dalai Lama as the head of state and a government was quickly elected.
Britain and Tibet signed a defensive pact and the US Guaranteed Tibet its independence. British bases were quick to open up in the nation to defend it from any attempted invasion by Chinese forces. No attempt was made, however.
Over the next few decades the elected government of Tibet who wanted to persue a centerist democratic future for Tibet frequently clashed with the Dalai Lama who wanted to persue a course of action "One half Buddhist and one half Marxist". So far the government has won out and Tibet has developed as a capitalist economy with much investment from Britain.
In the 1980s however, Margret Thatcher in return for China ceding Hong Kong to Britain, cancelled the Defensive treaty with Tibet and began withdrawing it's troops. the Chinese began mobilising, planing to retake Tibet as soon as the British had left the bases on their border. It is unsurprising then that Chinese Scout units were surprised to see that days after the British withrawel, the British bases were still funcioning, but populated with Indian Soldiers.
Soon after, India signed a treaty with Tibet almost exactly the same as the one it had had with Britain. Chinese generals were furious but could do little about it.
Since then Tibet has continued to develop, but much of its population is in poverty and in rural areas. It's military is small and largely made up of conscripts, with some middle range fighter jets that the British had 'accidentally' left behind.