*Mr. K quickly types out his missives while looking both ways for terrorists, RCMP, CSIS, CIA, FBI, AT&F...*
It has long been suspected that there have been a number of terrorist attempts prior to 9/11 which were unsuccesful due to the excellent work done by LE on both sides of the border and the domestic intelligence community. Prior to 9/11 the prevading theory was no news is good news rather than panicing citizens by telling them how close things came.
After 9/11, and because of the circumstances, you can be damn sure the next time they stop a major attempt, we will hear all about it, so that they can justify the Homeland Security Act and all the money the US has been spending to make things safer.
In the 70's and 80's terrorist organizations were successful in Europe primarily because they had loyal supporters in each country, and the various countries didn't cooperate well with one another. The same is not true today. The European Union, Interpol, MI5, SIS and many other agencies provide maximum cooperation.