Individuals in a population that normally compete with others for resources will compete even more vigorously for the same resources as they become fewer and fewer. The same process can be seen happening with other environmental factors such as light, dissolved oxygen, nutrients, and other factors. In general terms, what happens is that density-dependent factors have heightened effects as the population size increases, which result in regulation of the population size. These factors serve to limit population size no matter what the size of the population, and therefore work independently. Examples of density-independent factors would be climate and weather.
Human activities are notorious for affecting sizes of natural populations.
Note that these deaths would have occurred no matter what the population size was.