Nathu La is located on the Old Silk Route, an offshoot of the historic Silk Road. The Old Silk Route connects Lhasa in Tibet to the plains of Bengal to the south. In 1815, trade volume increased after the British annexed territories belonging to the Sikkimese, Nepalese, and Bhutanese. The potential of Nathu La was realised in 1873, after the Darjeeling Deputy Commissioner published a report on the strategic importance of mountain passes between Sikkim and Tibet. In December 1893, the Sikkimese monarchy and Tibetan rulers signed an agreement to increase trade between the two nations. The agreement culminated in 1894 when the trade pass was opened.