18th of March 1969 was more far more significant than 9/11
It was on that day that the greatest terrorist bombing campaign in history was launched. Lasting just over a year, it resulted in the region of half a million people being indiscriminately killed. It was also undoubtedly the most coordinated and expensive terrorist bombing campaign ever launched, involving as it did, carpet bombing by B52s.
Despite causing the deaths of hundreds of thousands of Cambodians, those responsible were never brought to justice for their crimes under international law. Needless to say as one would expect from a terrorist operation, the bombing campaign was a complete failure in which the terrorists failed to achieve their stated aims.