I'd also like to note that I don't really portray the Brazen Horde any particular way. They just show up and conquer the Bissel area.
Tavish the Great rallies people against them purely on economic grounds. He wants Thornward and the trade revenues from controlling the Fals Gap, and so do all the nobles who invested in Thornward with him. He doesn't care if they are Baklunish, Flan, Oeridian, or Suel. He wants the cash. It also provides a very secure border, and that is an even bigger plus.
Tavish the Blackguard just wants a conquest. Not being as truly charismatic as his father, or being able to convince everyone that yes, conquering a nation for his greater glory is indeed a useful thing, he defaults to that age old excuse for war - blatant racism. Even then he's still a bit too rational to actually believe his own rhetoric.
The real villains wind up being the Knights of the Watch. They transferred their anti-Flan racism (which was semi-justified as the order had been slaughtering Vecna worshippers for half a millenium) into anti-Baklunish racism at the drop of a hat, and embraced it thoroughly based on the cultural differences between civilized Keoland and nomadic Paynims.

However . . .
While there might be some slight parallel to the Crusades there is nothing of the Imperial era in the conquest of Ket (there is some in the conquest of the Pomarj), and definitely none in the liberation of Iraq (which might have a parallel in the conquest of Monmurg if Iraq was being conquered).
If you want a real world parallel for the conquest of Ket, you'd get closer comparing it to the Khmer Rouge seizing power in Cambodia, while the "liberation" of Ket is along the lines of the Taliban "freeing" Afganistan from the Soviet Union, or Iran being "freed" from the Shah by the Ayatollah Khomeini.