Sixty-five years after the landing of Allied forces at Normandy Beach, now known as D-Day, President Obama and German Chancellor Merkel toured the Buchenwald concentration camp in Germany with Holocaust survivor and Nobel Prize winner Elie Wiesel over the weekend.

More than 250,000 were imprisoned by the Nazis at the camp and roughly 56,000 died, including some 11,000 Jews. The camp was in operation for almost eight years until its liberation by Allied forces in 1945.

Many of the famous camps are already known but scholars are still working to uncover the full extent of the Nazi camp and ghetto system used in the Second World War. It's part of ongoing research at the United States Holocaust Memorial Museum.

The museum has just released the first volume of its "Encyclopedia of Camps and Ghettos." It's an attempt to document and catalog each forced-labor, prisoner-of-war, and death camp.

"What most people are familiar with are the major camps, Auschwitz, and Dachau, and Buchenwald, places like that. Most people don't realize that, for every one of those, there were dozens, hundreds, even thousands of other camps." Geoffrey Megargee, U.S. Holocaust Memorial Museum

"When we started the encyclopedia project, we thought we were dealing with 5,000 or 7,000 sites. That number is now at 20,000 or more, depending on what you count." Geoffrey Megargee, U.S. Holocaust Memorial Museum

"[The camps were] all part of the war effort for the Nazis. This was not a separate issue; it was not a separate effort. This was part of winning the war for them, both in terms of eliminating the Jews, in terms of enslaving millions of people for war production, and in terms of racially rearranging Europe, which was one of their primary war goals." Geoffrey Megargee, U.S. Holocaust Memorial Museum

1. What was the Holocaust?

2. Define concentration camp. Define a ghetto.

1. Does it surprise you to learn of more camps and ghettos from Nazi Germany? Why or why not?

2. Did you know about all of the different kinds of camps? Does this change your understanding of the war? Does it change your understanding of the Nazis?

3. The researcher said that this new evidence means that "no one could've ignored this at the time." Do you think that is true? Why or why not?

4. Why do you think that all this evidence is coming out now?

5. Do you think it is important to find out about all of these camps and ghettos? Why or why not?

6 Do you see any similarities between this research and other wars or conflicts you know about? What are they?