So party close attention.
So a bunch of Sunni Muslims attack a fictitious Christian country we'll call "Country A" and kill 3,000 of their citizens. They're from a fictitious place we'll call "Country "S". So, you feeble-minded tree mongers would conclude that Country A should declare war on Country S, right ? God, you're so naïve.
Thank God there's politicians to figure this out ! Now Country S has been feuding with the leader of a fictitious place we'll call "Country B". Because while Country B has a majority Sunni population, its leader is Shi'a and is suppressing the majority. Even worse than Mexicans terrorizing decent White people, but I digress. So Country S would desperately love to depose this leader, but they don't want to get their hands dirty. After all, they're still Muslim brothers in jihad against porcine Christians. So Country S convinces Country A to go to war with Country B under the guise of revenge for the terror attack actually promulgated by Country S.
Meanwhile, Country B's neighbor, a fictitious place we'll call "Country P" used to be friends with Country A, but then the puppet despot supported by Country A became finally too oppressive and self-serving and wad toppled in a revolution. This upset Country A quite a bit and they decided to install a new puppet leader in neighboring Country B to help them fight against Country P. While previously County A was helping Country P in its conflict with Country B, now it's helping Country B against Country P.
Country P has a majority Shi'a Muslim population and thus antagonistic toward Country S, but while they share the same religion as Country B, the population is of a different ethnic group and this explains the animosity. So Country P is still at war with Country B because of their majority Sunni population despite the fact that the leader is a fellow Shi'a and is disenfranchising those darn Sunnis.
So Country A invades Country B and kills its leader. So this pleases Country S but pisses off Country P majorly because now the hated Sunnis are in charge there. So Country P starts trash talking Country A.
Now enter a fictitious place we'll call "Country L". Their religion is sorta the same as Country A but they hate Muslims and Muslims hate them. Country L is one of Country A's closest allies and desperately wants Country A to smash Country P and Country S. But Country S is also a close ally, despite the fact that they bombed Country A in the first place. Country S also wants Country A to smack down Country P and Country L. Country A is pretty sure they now have a good reason to invade Country P.
Of course, that means obliterating two countries which had nothing to do with the original bombing attack.
But you know, In this fictitious place nobody can keep their penises in their pants, so "Country Y" and "Country D" both start civil wars. Country D receives support from Country U, which is a long-standing enemy of Country A but neither of them want to go to actual war with each other, so they make this civil war a proxy war just like in "Country K" years ago. So Country A decides to throw its support behind the rebels (aka "freedom fighters") and hope it goes better than it did with Country K where the freedom fighters installed an even more oppressive government than they were replacing and Countries N and C where the rebels won DESPITE the efforts of Country A supporting the government.
Country Y is a piddly little place that used to be two countries because they had a divided population, again half Shi'a and half Sunni, but a few years ago the two mortal enemies decided to reunite the country which obviously didn't work out very well (qv penises). Country A, still reeling from defeat of their albeit marginal efforts to restore peace in nearby Countries E and F, won't even mount a marginal effort there, also because their great friends, the bombers of Country S want Country A to stay out of Country Y.
So the question is; whom should Country A invade next to keep their well-oiled industrial military machine humming along ? Oh look, Country G ! Bonus: they're on the other side of the world, but their neighbor and protector, Country X, has been Country A's friend after Country A dumped their former staunch ally Country T which is the sworn enemy of Country X, but Country O is the sworn enemy of both Country X and Country G, but a staunch ally of Country A.
Fortunately of course, this is a totally fictitious scenario. In the real world, things are airways black and white.