Genocide is difficult, risky, and unnecessary, just look at how much flack Israel has caught by wiping the Palestinians.
All you need to do is re-define who votes -> And a government that is about to be conquered will rationally give EVERYTHING to those best able and willing to defend it, including exclusive voting rights.
"Those best willing to defend it" means men, because women who can fight a war are too rare to matter. And it means mono-ethnic because multi-ethnic armies are a catastrophe. So you just have to decide which ethnicity is going to defend you. You can forget about minorities because there's not enough of them (by definition), and you can forget about ethnicities which are not known for fighting ability. So by simple process of deduction you end up with "governments survive only by White men's willingness to defend them".
If we declare that our price is that we must have exclusive voting rights, then we will.
