Afghanistan was a country in Asia.
In the late 1830s, the British Empire occupied parts of Afghanistan, including Kabul, to halt Russian expansion in Central Asia which the British feared would threaten their rule in India. The Afghans rebelled against the occupying British forces, sparking the First Afghan War which lasted until 1842. The First Doctor, Susan, Barbara and Ian spent three months in Afghanistan in 1842. (PROSE: Mire and Clay)
The British Army was in operation in Afghanistan once again during the early 21st century. Danny Pink served in Afghanistan for five years (TV: The Caretaker) and was haunted by his experience of accidentally killing a young boy. (TV: Into the Dalek, Listen, Dark Water)