Taking land is the only way to win a war. Outlasting an opponent's ability/will to fight doesn't work at all, right?
Remind me: who controls Afghanistan? You know, that small country that didn't even have a standing army who fought against the most powerful military on the planet for 20 years ... after fighting the Soviets for 10.
Probably a fluke though -- it's not like that's repeatedly happened in wars across history.

Has sanitation, pest control, and medicine have advanced since the 13th century?
No ... we still need cats to do all the heavy lifting.