The best thing for you to do here is to ask your own instructor what he or she expects. Different instructors have different expectations on this subject.
My own rule is that students must cite sources whenever they are presenting me with facts that are not common knowledge. There is no need to cite, for instance, the fact that the Japanese attacked Pearl Harbor on December 7, 1941.
However, you will have to cite dates and facts that are less known. If you want to tell me the names of the aircraft carriers from which the airplanes flew to attack Pearl Harbor, you would need to cite a source. The same would apply if you were to tell me the exact numbers of American personnel killed or wounded in the attack and the names of all the ships that were damaged in the attack.
So, when you are writing a history paper, the common rule is that you do not need to cite things that "everyone knows." When in doubt, ask your own instructor whether you need to include a citation for a particular fact.
I agree. If you are citing the event, by actually stating it in your sentence may not have to cite it. However, if you are going to reference it more in general such as the "war" I would be more careful. Be sure to ask your instructor for specific examples as well. Sometimes, looking at exactly what it is they expect from you will be the best way to know for sure that you are following his/her directions. Good luck! Also, it may depend on what type of format you are asked to use.