There are many sources for the information in the collections of the research section and it would be impossible to list them all. Here are the most common ones.
Most texts and photos in the memorial collection that were not created by myself or my associates are from Wikipedia and Wikimedia Commons. Many of the texts for the list of wars also frequently cites Uppsala Conflict Data Program (UCDP) Conflict Encyclopedia.
The list of wars (and most of its fatality numbers) was based on the datasets listed below. See notes at the page of each conflict to determine the dataset used. You should be aware that this list is very much a work in progress and that information may be missing, inconsistent or contradictory. See the new FAQ for more information about definitions used.
Correlates of War Wars v4.0, 1816-2007. For most wars in the years 1900-1945. Bibliography Entry: Sarkees, Meredith Reid and Frank Wayman (2010). Resort to War: 1816 - 2007. CQ Press.
PRIO, The Battle Deaths Dataset version 3.0 (2009). For most wars 1946-1989. Bethany Lacina & Nils Petter Gleditsch, 2005. ‘Monitoring Trends in Global Combat: A New Dataset of Battle Deaths’, European Journal of Population 21(2–3): 145–166. This dataset use a preset range when fatality numbers are unknown and/or a best estimate can not be given. I've used the lower number in this range as a best estimate when calculating the total battle-deaths, which means that the numbers for this period may be much higher.
For almost all wars from 1989:
UCDP Battle-Related Deaths Dataset v.5, Uppsala Conflict Data Program, Uppsala University. Melander, Erik and Therése Pettersson & Lotta Themnér (2016) Organized violence, 1989-2015. Journal of Peace Research 53(5).
UCDP One-sided Violence Dataset v 1.4 - Eck, Kristine and Lisa Hultman. 2007. “Violence Against Civilians in War.” Journal of Peace Research 44(2). Melander, Erik and Therése Pettersson & Lotta Themnér (2016) Organized violence, 1989-2015. Journal of Peace Research 53(5). This dataset records fatalities from attacks on civlians by states or non-state actors where the number of fatalities in one year exceeds 25.
UCDP Non-State Conflict Dataset v. 2.5. - Sundberg, Ralph, Kristine Eck and Joakim Kreutz, 2012, "Introducing the UCDP Non-State Conflict Dataset", Journal of Peace Research, March 2012, 49:351-362. Melander, Erik and Therése Pettersson & Lotta Themnér (2016) Organized violence, 1989-2015. Journal of Peace Research 53(5). This dataset records battle deaths as a result of fighting between non-state actors, where the number of fatalities in one year exceeds 25.
There are several other sources for this section as well that are mentioned in comments to the fatality numbers:
Matthew White's website Necrometrics has many carefully calculated comparisions of death toll data from diverse sources, which are very useful when it comes to estimating excess deaths.