Yes, of course, everyone who is attacked will fight back. Obviously.

What if, however, you imagine that you have been attacked by A....because yours news media and leaders told you so....but there actually was no real attack by A. The attack was either completely illusory (never really happened) or was by someone other than A (might be a false flag attack...a deliberate setup by your own government or some "friends" of yours who arranged it).

That has occurred before in history, and it will undoubtedly occur again. It's been done many times. A provocation is needed to get a war going, so one is provided.

What you have happen is that millions of people then unwittingly get taken in, they think their country was attacked by A, and off go the troops to invade A, and it's all just an illusion.

Governments are quite clever at arranging such things.