now you're being far too literal.

it is in the eyes of the recipient to judge whether the host nation is tacitly complicit or otherwise incapable in stopping terror attacks that originate from within its own borders, and its it the eyes of the rest of the world to judge whether the recipient has been over-hasty in apportioning 'criminal' blame to the host nation.

we never invaded southern ireland over cross-border terror attacks from the ira.

but none of that changes the fact that a nation is reponsible for controlling the activities of its citizens in respect to their actions against a neighbouring country. casus-belli is the accepted response to such actions, it just calls for a little judgement, like whether or not a nation has any ability to stop such attacks, if not then can the recipient stop such attacks with military strikes against the terrorists or via regime change.