If you scroll down to the references of a page, say, Adolf Hitler's, you will find numerous sources of which many can be found in university libraries. I would know because I regularly visited my university library in the five years that I studied there.Wikipedia is an open source encyclopedia and thus not a substitute to a visit to a university library.
Wikipedia does not claim to be a source for historical documentation.
Wikipedia has put Encarta out of business. Encarta. Why do you think Wikipedia is unreliable if it is regularly moderated and been able to put a major encyclopedia program out of business?