You are correct, from my understanding, in that a variety of factors from population density, to agriculture and animal domestication led to a greater spread of diseases. Even in analysis of native american populations before European contact we see that diseases increased when population density increased [1].
The other factor that hasn't been mentioned is that a disease can be deadlier when the population density is higher. The disease can find another host to infect before the original dies and still stay active. Whereas in a situation with spread apart populations the deadlier variant would die out once the small local population was killed.
The European diseases carried this much deadlier profile and thus were more effective in killing native americans than native american diseases were in killing americans.
The other factor that hasn't been mentioned is that a disease can be deadlier when the population density is higher. The disease can find another host to infect before the original dies and still stay active. Whereas in a situation with spread apart populations the deadlier variant would die out once the small local population was killed.
The European diseases carried this much deadlier profile and thus were more effective in killing native americans than native american diseases were in killing americans.
1. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1071659/