Rivalry grew steadily over Central Asia in the Great Game of the late 19th century. Russia desired warm-water ports on the Indian Ocean while Britain wanted to prevent Russian troops from gaining a potential invasion route to India. In 1885 Russia annexed part of Afghanistan in the Panjdeh incident, which caused a war scare. After nearly completing the Russian conquest of Central Asia (Russian Turkestan) the Russians captured an Afghan border fort. Seeing a threat to India, Britain came close to threatening war but both sides backed down and the matter was settled by diplomacy. The effect was to stop further Russian expansion in Asia, except for the Pamir Mountains and to define the north-western border of Afghanistan. However Russia's foreign minister Nikolay Girs and its ambassador to London Baron de Staal in 1887 set up a buffer zone in Central Asia. Russian diplomacy thereby won grudging British acceptance of its expansionism. Persia was also an arena of tension, but without warfare.