The terrorism that came from the American skies on September 11, 2001 needs no introduction to anyone. The astrological transits to the USA's natal chart for this day are probably equally well known to most astrologers - Mercury was conjuncting natal Saturn (0°27app) whilst being trined by transiting Saturn and sextiled by transiting Pluto, and Uranus was trining natal Mars (also 0°27app) .
Predictably enough, it wasn't too long before someone cooked up a "prophecy" by the sixteenth century seer Nostradamus which was said to predict the events in question. They lumped together various couplets from various different verses by the Frenchman and it was duly reproduced by the tabloid press who demonstrated their usual capacity for in-depth, vigorous research. It was very reminiscent of the way they had publicised his so-called "end of the world" prediction in the summer of 1999, when they had conveniently overlooked the fact that he had written no such thing and was actually referring to the solar eclipse in August of that year.
Interestingly, this prediction (Century X, v.72) was one of those disected to provide part of the fake September 11 prophecy, the middle two lines of it looking very apposite:
Another plundered quatrain was Century VI, v.97:
Again, you can see why it was used, especially if you take the British and the Americans to be the descendants of the Normans (via William the Conqueror). Erika Cheetham, author of a popular and long standing English language edition of Nostradamus' Centuries, had long ago associated this verse with New York, pointing out that New York state extends to 45°North, and this is where we take our point of astrological departure.
The aforementioned solar eclipse of 11 August 1999 had its centre of totality bang on the 45th parallel north of the equator, and since then there have been no more eclipses visible in our northern hemishere. Thus we can take this one to have some astrological importance.
Drawing up a chart for this date, we find the eclipse itself is semi-square (0°15 sep) the USA's natal Venus, Uranus is trine their natal Saturn (0°08 sep) and Pluto is trine their natal North Node (0°09 app). All very well, but as we know, nothing particularly earth-shattering happened to the US that summer, or indeed any other country despite the apparent malignancy of the aspects [Saturn opposite Mars on the horizons, square the Eclipse] at the point of totality. Rather, it seems that potentials were set up at this time, waiting to be triggered off later, for if you scroll forward and compare this chart with one drawn up for what became known as First Strike on September 11, 2001, some very interesting things emerge.
Firstly, you notice that the Sep 11 trine between Mercury and Saturn (which was apparently symbolising the strife inflicted on the US natal chart) is turned into a composite Grand Trine by 99's Uranus, at 14° of the Air triplicity. This ties Sep 11 to 99 in a knot of upheaval (Uranus) and constriction (Saturn) through air travel (Mercury/Air), all feeding into the US horoscope via their natal Saturn in the tenth house. It's hard to see past Saturn's traditional image as the scythe-bearer in this instance. Michael Baigent (Mundane Astrology, p477) sees this natal point as representing the American preoccupation with national honour, and their need to be "the greatest country in the world", and these terrorist attacks certainly shook that adolescent sense of invulnerability to its foundations.
A second interlinking of the charts for '99 and Sep 11 echoes a relationship between the US natal and '99 itself. Pluto at the time of the eclipse was trine the US North Node, as we've seen. What's interesting in light of the North Node's role as an indicator of future trends and patterns is that Pluto on Sep 11 was trine the eclipse's North Node (0°01 sep). This Plutonian transformation feeding through Nodal future trends twice in exactly the same manner, and combining with the Mercury-Saturn configuration on Sep 11 via a sextile (1°42 sep) suggests this truly isn't just a random confluence of dates. Indeed, Sep 11 also saw Venus conjunct the '99 eclipse (0°06 sep at First Strike) and Mars trine the eclipse's Venus (0°41 sep). Quite how you interpret a solar eclipse's natal points is open to conjecture, but I imagine the tightness of these transits serves to underline just how strong an indicator of future events such a thing can be.
Given this, the question has to be, could we have predicted something along the lines of these terrorist attacks from the astrological interactions between this eclipse and the US national chart? I strongly doubt it. The semisquare to natal Venus whiffs a bit, but is hardly counted as a major transit. Perhaps you could glean something from the Pluto trine Node repetition, but the perception of a trine is that of a benevolent configuration, and the combined Grand Trine would probably only have enforced this view beforehand. Pluto is an especially difficult planet to fathom - certainly its brute power is evident in this scenario, but you would likely envisage a trine as channelling this quality constructively. One could argue that in the aftermath, New York and America as a whole came together as a community like never before, but that's the silver lining to a very black cloud, a cloud that astrology would far more likely have attributed to a hard aspect than a soft.
Perhaps the composite Grand Trine's placement in the Air signs would have suggested some aviation theme, but the presence of Uranus and Mercury would probably have hinted more at some revolutionary development in telecommunications or suchlike. It seems to be the case, as with the verses of Nostradamus, that astrology is only capable of pinpoint accuracy in retrospect.
Which brings us back to the Seer of Salon. What's with these predictions of his - if VI:97 is indeed referring to Sep 11 and X:72 to the eclipse of '99, can we take the latter's first line mention of "seventh month" to have a double meaning? The eclipse fell in July according to the Julian calendar of Nostradamus' day, but was he also referring to the old latin seventh month of September? Or were all those nines referring to September, modern style? If his "king of terror" is Osama Bin Laden/Al'Qaida, and if he's mentioned them in the same context as the eclipse, was he aware of the astrological connections between it and Sep 11? It all seems vaguely possible until you recognise that the interlinking relies upon Uranus and Pluto, two planets unknown in sixteenth century France. Plus, by most contemporary accounts, Nostradamus was an intuitive first and an astrologer second - his horoscopes and almanacs were commonly lacking technical accuracy (see Nostradamus Astrophile by Pierre Brind'Amour). Even if you suggest that a prophet could foresee the future discovery of new planets, it's unlikely that this particular prophet would've had the inclination to tabulate their movements as well!
If he did foresee the attacks of Sep 11, perhaps it could have been as the result of extrapolation from the '99 eclipse, or perhaps he just pinned his vision to the nearest, and most likely looking, eclipse. Or perhaps, as his critics have been saying for nearly half a millennium, he wrote so many verses and with such ambiguity, that they are bound to coincide with actual events occasionally.
Whatever your view, the astrological links between the formation of the USA, the 1999 solar eclipse and the attacks of September 11, 2001 are there for anyone with the appropriate software to see. They suggest that solar eclipses can be a useful tool which merits further study in the field of Mundane astrology. (Though I admit a genuine talent for prophecy would probably be far more useful...)

Charts (using Astrolog v5.41F)
September 11, 2001 8:46am local time, New York 74W00 40N43
Solar eclipse August 11, 1999 1:08pm local time, centre of totality 24E18 45N06
USA July 4, 1776 5pm local time, Philadelphia 75W10 40N00 (several different times are argued for the US national chart, but this is immaterial to the natal points used here)

Bibliography
"Mundane Astrology" by Baigent, Campion & Harvey; Thorsons 1995 edition
"The Final Prophecies of Nostradamus" by Cheetham; Little, Brown & Co 1993 edition
"Nostradamus Astrophile" by Brind'Amour; University of Ottowa Press 1993