It seems that there was, in some locations such as Europe, a large-scale 'replacement' of native populations by Yamnaya or Indo-Europeans. The closest analogue in modern times we have is the European peopling of the Americas, with diseases like Smallpox being a huge component to the course of events. Could smallpox, itself, have been responsible? Would it have had a significant impact on urbanized centers during the Bronze age that may have contributed to the worldwide 'Bronze Age Collapse'?
Even more so now since COVID, I find the idea of how disease has impacted human culture so fascinating and underappreciated. I'd love to learn more about it.