There used to be two rules of successful imperialism. First, don’t invade Russia. Second, don’t invade Afghanistan. As Rodric Braithwaite points out, invading the latter country itself offers no real difficulties. The Afghans abandon their strongholds and take to the hills, allowing the invader to enjoy the illusion of power in Kabul, with a puppet leader installed in the Bala Hissar, the old palace fortress.