I don't know what to make of your post. You have "seen some offensively transparent excuses to start military invasions" and yet keep asking these naive questions.
A plane was travelling between two countries. The head of state of a third country gave the direct order to hijack said plane in order to murder someone onboard.
I can't see how you'd interpret that as anything except an act of war. That doesn't seem like an offensively transparent excuse to me. Certainly in comparison to "My fortune cookie said they might have WMDs" or whatever the line was two decades ago that was apparently good enough for the US.
I'd say "what does it take, a literal invasion?" but that already happened in Crimea.
