In Vietnam, the Politicians determined and dictated the pace and
conduct of war on the ground.
The Commanders in the Field and actually on the Ground had little
power to dictate which target holds priority.
Many strategic military targets that should have been destroyed or
neutralized were made OFF-LIMITS by the Politicians - for fear that
the war will be enlarged by hammering the Vietnamese so badly that
it will draw the direct support of the Communist Chinese (as had
happened during the Korean War).
With the Field and Ground Commanders fighting the war with "one
hand tied behind their back", the Vietcong and the North Vietnamese
Regular Soldiers had a field day.
Surprisingly enough, after the war, it was found that had the
Americans persevered they would have knocked the teeth out of the
Vietnamese, and got them to sign a peace treaty with more favorable
terms that ensured the independence of South Vietnam.
The Vietnamese had played poker with the Americans and won - much
like General Yamashita during WW2, who bluffed the UK General
Perceival into thinking that the Japanese had unlimited logistics
when actually their ammo was low, and their manpower was less than
the UK forces put together defending Singapore.
Surprisingly enough, through casual conversations with common
people living in the north, many were simple rural folks who are
largely apolitical and were mostly sick of the communist concept of
nationhood; and were waiting in anticipation for the US led forces
to sweep upwards across the North-South DeMilitarised Zone
(DMZ).
Unfortunately, the Communist International Movement manipulated the
anti-war public opinion that was gaining fashion in the USA; and
helped speed up the antagonistic feelings of the US citizens
against their own government.
Hence, forcing the US Government to negotiate a shameful withdrawal
of their military presence in South Vietnam, that finally led to a
debacle on a grand scale, that was never seen in military history
during this modern 20TH Century.
The rest is history.
In Afghanistan, and during Dessert Storm too, the Field Commanders
(who experienced the 'hands tied behind the back' interfering
policies of Smart Ass Politicians) are now in command, and sitting
in the chairs of those 'Smart Ass Politicians'.
Having learnt the Vietnam Lessons of "How Not to Fight a War", they
allowed a great degree of command independence, after setting the
General Goals.
In Afghanistan, the world opinion was largely in favor of the US,
except from the Islamic Countries - who demanded for hard evidence
of the 9-11 works being the work of Osama Bin Laden with the help
of the Talibans.
Now that the evidence have been found, and more evidence are being
produced, the Islamic World seems to have gone dumb, and still
disbelieving.
Besides the differences in terrain, the major factors that have
made these distinct differences in the two scenarios that produced
two different results are well accepted and espoused by quite a few
military analysts.
Visit the National Library, and you can research more on how the
conduct of these two wars have been made.