What events might Pieter Bruegel the Elder have witnessed or heard about that would have inspired the horrors and desolation depicted in his masterwork "The Triumph of Death"?

by AclockworkWalrus

https://upload.wikimedia.org/wikipedia/commons/1/10/Thetriumphofdeath.jpg

punninglinguist

Much more specific follow-up question: what is that musical instrument that the skeleton perched on the cart full of skulls is holding?