The official reasons were: 1) Iraq weapons of mass destruction, 2) Iraq connection with terrorism and 9/11, and.... well, that's pretty much it.
Of course both reasons didn't hold up over time. (Many of us Americans still view, rightfully I think, that both reasons were 100% BS from teh start.) But they were 'persuasive' enough to justify the war in the eyes of Congress. In BM you have to give reasons that convince the nobles who will be fighting the war and who can (theoretically) oust you from power if they don't take kindly to it.
You just need to throw dust in people's eyes to begin the war, and then you'll have an army of rednecks and cowards both fighting tooth and nail to prevent the humiliation of admitting they were wrong and/or appearing cowardly for pulling back.
