>>>>>Nonetheless, Afganistan got invaded as result of BinLaden spending some time there. It was as justified as bombing chain of Hilton hotels where I am sure he stayed at some point, before going caves.
>>>...
>>>>They were harboring the terrorist responsible for the deaths of 3000 Americans. The attack on the World Trade Center was an act of war.
>>>
>>>Now in the early seventies SFR Yugoslavia was under several terrorist attacks (a heavily armed group of about 20 terrorists inserted in the middle of tourist season; a passenger plane exploded above Chechoslovakia, a bomb in a full movie theatre in Belgrade, ambassador in Sweden assasinated, to name a few). However, Yugoslavia did not even think of attacking any of the West European countries which harbored the executors of these attacks, nor were they much prosecuted in those countries. The latter short of stopped when they started hitting on local police and politicians.
>>>
>>>Nobody even mentioned the words "war" and "act of war". But if the Yugoslav authorities had done it at the time, what do you think, would that have been justified?
>>
>>I'm afraid I do not know enough about this to make an educated judgement.
>
>Simple as that: several West European countries were harbouring terrorist groups, which then attacked a sovereign country several times. Would this counry be within its rights if it claimed these attacks to be "acts of war"?

I know there's a twist here but I'll bite anyway.

Were these West European countries asked to hand over the terrorists and refused? Were they working in conjunction with one another? State-sponsored? If so then yes theis is clearly an act of war. If the terrorists were merely residing in the country despite their best efforts then no.