I'm doing a plagiarism quiz. if I read information on Wikipedia that tells me the years World War II was fought and which countries participated in the war. If I include these facts in my paper without showing that these facts came from Wikipedia, is this plagiarism?
In this specific case, you should not have to cite Wikipedia. The only reason to cite Wikipedia would be if you were including some of the countries that were officially involved in the war but which really played only a tiny part and were therefore not important.
The reason for this is that there is an exception to the need to cite sources if the information you got from the source is something that can be seen as common knowledge. There are certain facts that essentially everyone knows. There is no need to cite sources for such facts because everyone already knows them. The dates that World War II began and ended are common knowledge. Essentially everyone who is educated knows that the war began in 1939 in Europe and in 1941 for the United States. Everyone who is educated knows the war ended in 1945.
With the countries involved, it is a little more complicated. Almost everyone knows that the US, the USSR, France, and England were the main Allied powers and that Germany, Japan and Italy were the main Axis powers. You should not have to cite sources if you list those countries. However, if you start to list more obscure countries (like Brazil, which was on the Allied side), you are better off citing your sources.
Please refer to the purdue.edu link below for more on how to determine if something is common knowledge and does not need to be cited.