Agreed. I don't know of any modern army that has been defeated by guerilla forces. And you are correct that Tet pretty much wiped out the NLF guerilla forces. But in a larger sense, Tet also defeated the U.S., making possible the later victory of the NVA over the South Vietnamese army -- that is Tet made the eventual withdrawal of the U.S. forces inevitable.
> So when
> else did unconventional forces defeat a sustained US
> offensive?
Agreed. Never. But "sustained US offensive" is not, under present conditions, a given.
> I don't count Lebanon or Sudan, because the
> US cut and ran when it faced casualties in those
> cases.
You should. The only difference was a difference in the level of casualties the US was prepared to take. We do not _know_ at this time either what the level of casualties will be in Iraq in 2005 _or_ the level which the US, at this time, can bear. Hence your next statement
> In Iraq it seems willing to bear those casualties
is speculative: "those casualties" is a wholly unknown quantity, in respect to the number to be expected, in respect to the US capacity to bear, and in respect to political conditions in the US. The collapse of the US Army in Vietnam was grounded _both_ in the casualties inflicted by the NVA _and_ in political conditions at home. That is, we have at least three variables.
1. the number of casualties the Iraqi resistance will be able to inflict on the U.S. army. (This is related to the principle that a guerilla movement need not "win" but "survive.")
2. the size of the U.S. army needed to maintain a "sustained U.S. offensive"
a. Where do the troops come from? (Possible need for draft?)
b. Where does the equipment come from (equipment is apparently wearing out more quickly than anticipated, suggesting that the financial burden of the war may grow yet greater)
3. What kind of anti-war effort can be mounted in the U.S., as that will greatly condition the u.s. capacity to sustain whatever level of casualties the Iraqi resistance can impose. The stronger the anti-war effort at home (and globally), the lower the level of casualties that will be acceptable.
These factors are tightly interwoven, and it is incorrect, I think, to consider any one of them in abstraction from the others.
A fourth factor might be phrased as "How many casualties are available u.s. forces willing to impose on the Iraqi civilians?" It was not until after Tet that serious opposition to the Vietnam War begain to grow _within_ the military. But a core of resistance has existed within the present military since the Afghanistan aggression.
Carrol