Judith, which countries are you referring to? Google tells me that the UK, USA and Germany all have much, MUCH lower population densities nationally than Rwanda, Vietnam, or Sri Lanka. If you're talking about places like Mongolia or Ghana, the opportunities for self-isolation and social distancing in these countries (and their densely populated major cities) are much lower than in the western nations I just mentioned. If I compare my home country (extremely sparsely populated Australia) with my current country of residence (much more densely populated Ghana), the difference in death rates may in part be due to difference in demographics, but is also heavily influenced by differences in public health mis/management and adoption of preventative measures by the populaces of these two places.