The information available in the collections presented in the research section of this website has been gathered from numerous sources, and it would be impossible to list them all. This page contains a selection of the most frequently used sources.
Please note that the list of wars since 1900 is very much a work in progress and that some information may be missing, inconsistent or even contradictory. This collection uses with few exceptions the widely used academic definition of a war as being an armed conflict (interstate or intrastate) with at least 1000 battle related deaths in one year - where a state is one of the belligerents.
It should also be noted that the estimated death toll for each conflict should be taken as a very rough estimation. It is in most cases impossible to get the exact death toll for a given conflict, and there are many ways to define what kind of deaths should be included in such numbers. Many academic institutions includes only "battle-related deaths" (military and civilian) - i.e. deaths that occured as a result of fighting between the parties, while others include also indirect deaths caused by disease, famine or terror that occured as a result of war.
The estimated death tolls given in this list use both definitions. The definition that includes both battle-related and indirect deaths is the most commonly used - and it is the dominant one for conflicts before 1975.