First of all, it's Sixth Column. Secondly, the "white people" were the remnants of the US military after the United States had been invaded and conquered by a pan-Asian bloc that emerged that had previously conquered and absorbed the Soviet Union. The religion was just a ruse to cover their rebellion. They beat the invaders using a sci-fi mcguffin that, among other implausible things, could selectively be tuned to kill based on genetics.

It's among his weakest novels but I'm not sure how anyone would derive "genocide" out of it. IIRC, it was a plot point that the invaders also treated Asian-Americans brutally.