These are concise overviews of the refugee situation worldwide.
Background on Ethnic Groups
This encyclopedia offers overviews of ethnic groups in the United States. It will discuss if a large group came initially as refugees, but it isn't going to discuss the current situation.
If you wanted to learn more about an ethnic group, or a past event, try:
Try looking for books on your topic, and skimming over the introduction and table of contents of relevant titles. The introduction usually offers similar background/overview information as the above sources. Or there may be a chapter that's very relevant and worth reading.
Other organizations that offer overviews of the situations, including what is happening locally.