Let's communicate more clearly than the OP did: The
US could have won in Iraq in Gulf War I and II and
in Afghanistan. How? Kill everyone who resisted.
How? That's the strange part: For US military
technology, killing lots of people is nearly as easy
as pushing some buttons. E.g., an Iraqi officer was
amazed -- praise from an adversary is especially welcome:
There was an Iraqi tank parked tightly between
two buildings, and the US put a missile on the
tank, destroyed it, and didn't hit either of the
buildings. The officer said: "American military
technology is beyond belief". Well, it was to him.

The biggie point was, the US didn't want to kill that
many people in Iraq or Afghanistan. Instead a main
goal was to help them get a good constitution, elections,
elected government, government of laws instead of
something else, freedom of speech, the press, assembly,
religion, have well trained police,
etc.,
roads, schools, hospitals,
move into the 20th, maybe the 21st century, become
a good member of the nations of the world,
etc.

Why that goal? Because the US does not want to
be seen as an imperialist or colonial power
or an occupying force. Instead US policy
since WWII has been to help US security
by having other countries be democratic
with strong economies hoping that that combination
will keep down shooting.

Indeed, after Gulf War II, W was against
doing a lot to occupy and govern Iraq and, instead,
stated that
"The Iraqi people are perfectly capable of
governing themselves." Well, not exactly
"perfectly"; maybe after some civil wars, etc.

Well, for the cases the OP mentioned, that
US goal of democracy, etc. flopped.

Why flopped? In both cases, Islam had more power
to run the place than anything the US brought
unless the US just killed a lot more people,
likely most of the Mullahs. The US didn't want
to do that. Could the US have done that? Sure:
Easily. Just push some buttons. Trivial.
But would also kill a lot of dogs, cats,
women, children, peaceful people, etc., say,
like the US did in WWII fire bombing cities
in Germany and Japan, or, say, like
Germany did in their bombing of London,
Warsaw, etc.

Actually one broad lesson is that actually
freedom of speech, the press, assembly, religion,
etc. is often much less welcome, sometimes
even in the US,
than the
US founding fathers assumed!
The core of such freedoms is that
people need not conform. Alas, a too
common response to differences
from such freedoms
is to pull a trigger or plant a bomb.

Saddam said that we'd have a heck of a time
keeping Iraq together -- we're learning that
now. Saddam did keep the place together, but
he borrowed from the Stalin playbook. The US
thought that that was cruel -- it is. But
maybe more Iraqis have died per month since
Gulf War II or I than before it.

Maybe what Joe Biden often said would be the
right stuff -- partition the place into
separate regions for Sunnis, Shiites, and Kurds.
With some irony, one interpretation of what
is going on now is just that.

In Iraq and Afghanistan, the Mullahs are
not much afraid of US weapons because
they know that the US would be reluctant
to kill enough Afghans to make those weapons
defeat the Mullahs.

But for someone like a Saddam who wants
to have a big army, air force, etc.
and invade their neighbors, as in Gulf War I,
the US can win in six weeks of bombing and
100 hours on the ground.

For any country that wants to use nuclear
weapons, the US still is awash in
weapons only "have to use once".

In Viet Nam, the situation was similar but
otherwise somewhat different: The US
could never find anyone to support in Saigon
who could also get enough support of
the people of South Viet Nam.

But in Viet Nam, the US could have won there,
too: Just be willing to kill a lot more
people. Sadly, a lot more, even a lot
more than we did kill, which was
sad enough.

When my HP laser printer quit,
I got a Brother printer. It's terrific,
and it's made in Viet Nam. Good for
Viet Nam.

I never understood just why the US
had so much trouble in Viet Nam:
We should have been able to have
sat down with Ho and cut a deal:
The US will give you a lot of stuff,
darned near anything you could want
in products, technology, universities,
medical care, development loans,
roads, bridges,
hydroelectric facilities,
telephones, good trade agreements,
South Viet Nam, etc. if you would
just quit going to Peking and Moscow
for free lunches and trash talking the
US. Should have been a good deal for
both sides.

For Iraq? Just sit down with Saddam
and make him an offer, personally,
one on one, he couldn't refuse.

For the German Tiger tanks, from all
I've understood from the history,
the US managed mostly to avoid the
Tiger tanks in tank to tank battles.
Instead: (A) We avoided those tanks,
e.g., during the Normandy invasion,
due to US air superiority, the Germans
had a tough time even getting Tiger
tanks to Normandy. (B) Otherwise
in Europe, the US killed Tiger tanks
heavily from the air, e.g., from
P-47s. (C) Otherwise, say, in North
Africa, the US used artillery.
In the Battle of the Bulge
maybe the Tiger tanks were low
on fuel.

Maybe the Tiger tanks were in
a "battle of attrition" tank to tank battles
with Russia at Kursk.

Broadly in conventional war, win the air battle,
and the rest is routine and not in doubt.
That's what the US did to both
Germany and Japan and to Saddam in Gulf War I.
And that's what the Battle of Britain
was about: Germany knew that they had
to win the air war before invading
England, Germany was not able to
win the air war against the British --
mostly because the German planes did
not have enough range.

And, in short, winning the air war is
the purpose of the
F-22 now.