You already know how helpful it is to get some background information on your research topics. Wikipedia is often the default because it's so easy to find an entry and the entries are often helpful.
That said, the quality and reliability of Wikipedia entries is not something you can count on. In addition, most Cornell instructors will tell you that you cannot cite wikipedia entries.
The rules for a good Wikipedia entry are: No statements of opinion and every statement of fact must be referenced to a source. A Wikipedia entry is only as good as they sources it cites. Follow the source notes to verify the information.
For this course, you may want to browse or search some of the library's online subject encyclopedias listed here. Admittedly, they are not as easy to search, but the quality of the entries is often worth the effort. In addition, the entries are signed by the author and include a citation.
Selected Reference titles on Colonialism
The digitized edition of the Encyclopedia of Western Colonialism, above, is available via Emergency Temporary Access from HathiTrust. Scroll down the record and select a link. (It doesn't have to say "Cornell!"), then scroll to the top and "Check Out."