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I'm flying just a couple of hundred feet from the ground

in an American black hawk helicopter

along walk stretch of the vast border between Afghanistan and Pakistan.

You get a really good idea of just how vast and how difficult the terrain is

for fighting and insurgency.

There are deep valleys, the snow, everywhere, high peak mountains.

Even as conditions are at the moment,

if winter fighters can cross from here,

over the border into Pakistan and sanctuary.

But the winters are at least quieter

and they give the military commanders the chance to use the lull

to strengthen efforts to try and win the people over.

Among almost 40 nations and with more than 40,000 troops,

there are many different tactics.

But America, with a lion's share of resources,

is driving the process.

Vague historical theories of counter insurgency

have been sharpened into a field manual,

being followed to the letter by US forces.

...