How about that India is majority Hindu, while Afghanistan has long been noted for its particular brand of mullah-inflamed Muslim fanaticism? The British never had any more than about 200,000 people among India's population of millions - many of them civilians such as doctors, missionaries and officials in very vulnerable, isolated areas - and yet they never experienced widespread terrorism against them, even in the bitterest depths of the independence struggle.
   Incidentaly the British repeatedly got absolutely nowhere trying to pacify Afghanistan (they wanted to instal a fiendly puppet ruler - sounds familiar!- because, quite rightly as it turns out, they were worried about Russia's intentions in that area.) One of the main reasons they got nowhere because of the extreme Muslim fanaticism of the population - read some Kipling or the numerous non-fiction histories of the time! Muslim fanaticism long pre-dates meddling by Britain and America, but the modern world has given them better tools and a diaspora to work with.
   British soldiers in Afghanistan had no illusions about what would happen to them if they were caught - being beheaded was the least of it, they could expect to be castrated (usually by the women) have their mouth urinated in until they drowned, be pegged down on ant nest or even be flayed alive - as Kipling wrote (more or less)

          When your lyin' out wounded on Afghnistan's plains
          And the women come out to cut up your remains
          Just you roll to your rifle and blow out your brains
          And go to your God like a soldier.

The Afghans did not do this to fellow Afghans - then as now they were in a perpetual state of war amongst themselves - this was a religion-inspired response to infidel invaders. Sound familiar?
    I note you did not respond to my second post. And why should we pick on the USA all the time? China is a disgusting imperialist, killing about 1.1 MILLION Tibetans since they invaded. Ever heard of a Tibetan terrorist?