REFERENCE WORKS: Generally, the category of works we call "reference" includes atlases, almanacs, bibliographies, dictionaries, directories, encyclopedias, guidebooks, handbooks, indexes, manuals, yearbooks—materials we "refer" to rather than read entirely. Go to these for definitions, topic overviews or background information. Reference librarians can help you find these.
Ethnic history is a branch of social history that studies ethnic groups and immigrants. Oscar Handlin (1915-2011) might be considered the father of ethnic history. "He ranks as one of the most prolific and influential American historians of the 20th century, with pioneering works in the fields of immigration history, ethnic history, and social history."
[Oscar Handlin. (2004). In Encyclopedia of World Biography (2nd ed., Vol. 7, pp. 121-122). Detroit: Gale. Retrieved from Gale ebooks]
Early in his nearly half century career as a history professor at Harvard, his most influential work,The Uprooted: The Epic Story of the Great Migrations that Made the American People, won the 1952 Pulitzer Prize in history.
[Kraut, A. M. (2013). Oscar Handlin and "the Idea That We Are a Nation of Immigrants." Journal of American Ethnic History, 32(3), 26-36.]