Poland ! I was alluding to the fact that the Plague wasn't uniform and that if demographic depression were an incentive to invade by itself, places that were unaffected (like Poland) would have expanded.

Instead Poland repeated the exact same pattern that had been pioneered in Gaul, then picked up by the Germans : expend East, where the Plague didn't have much effect, into non-Christian land and implement literate administration, centralized religion and feudalism.

The fact is the Black Plague didn't pose an existential threat in Western Europe, and it seems even else in other urban regions. I remember a historian, perhaps Le Goff or Leroy-Ladurie, remarking that the most astonishing thing about the Plague is that it changed nothing. The archives looked the same before and after. Just business as usual. In that sense the Thirty Years War was far more destructive.

All that to say that disease, as large as it gets, in itself isn't enough to sink well established institutions. And it's not a good enough argument to strip the Spanish of any credit in the conquest of the Americas.