sentences:  This led to Persian troops, along with their Russian allies, attacking the city of Herat in western Afghanistan in an attempt to annex it.Russia, wanting to increase its presence in South and Central Asia, had formed an alliance with Persia, which had territorial disputes with Afghanistan as Herat had been part of the Persian empire and had only been taken over by Afghanistan in 1750.Lord Auckland's plan was to drive away the besiegers and install a ruler in Afghanistan who was pro-British.