In terms of "massive devastation", scaled for population, I strongly suspect the Thirty Years War will give either World Wars a run for their money in the area over which they were fought. It certainly left very deep scars that were felt up to WWII....

Echoing your point, the Napoleonic Wars ended 99 years before the start of WWI: https://en.wikipedia.org/wiki/Battle_of_Waterloo The precursor wars which very much were an input into WWI ended less than 45 years before: https://en.wikipedia.org/wiki/Franco-Prussian_War (and I'm in the camp that primarily blames France for initiating WWI).