 Complete the following phrase:  Anglo-Chinese Convention Relating to Sikkim and Tibet, which Tibet disregarded since it was for Lhasa alone to negotiate with foreign powers on Tibets behalf. The British concluded in 1903 that Chinese suzerainty over Tibet was a constitutional fiction, and proceeded to invade Tibet in 190304. The Qing began taking steps to reassert control, then invaded Lhasa in 1910. In the 1907 