I'm fairly sure most people died of illness or "old age" but do we know if any specific illnesses killed more than others? Was it mostly infections that did people in or were factors such as heart disease also of significance? If infections were the main culprits, do we know if they were respiratory or circulatory?
Also, were plagues common and widespread enough to be a significantly common cause of death (with the exception of the Black Death?
Prior to modern medicine infectious diseases was the most common cause of death. It's still that way in the third world.
The fear of antibiotic resistant bacteria is that we'd go back to that.
Everything else you mentioned was still a factor though they were much less understood of course.
Cancer has been around since ancient times but became the most common cause of death because modern medicine made more people live long enough to get it.
Sorry for the lack of finer detail. I mostly just know that the black death was hardly the first encounter with bad plagues.
Childbirth used to be a significant killer of women and infants.
And yes, bacteria were a rather big deal before the discovery of antibiotics. In certain times and places, viruses were also significant, e.g., smallpox hit some Native American societies rather hard after it was brought over here by Europeans. But taking the scope of history as a whole, bacteria were usually the bigger deal. Just to give one example, the one we now know as "strep throat" was, before you could easily go to the doctor and get pills to eliminate it, often deadly; they called it "scarlet fever".
There's also warfare. Plenty has been written about that.