Ridge, M., & Billington, R. A. (1969). America's frontier story: A documentary history of westward expansion. Holt, Rinehart and Winston.
Lua i Stíl Chicago (17ú heag.)Ridge, Martin, agus Ray Allen Billington. America's Frontier Story: A Documentary History of Westward Expansion. New York: Holt, Rinehart and Winston, 1969.
Lua MLA (9ú heag.)Ridge, Martin, agus Ray Allen Billington. America's Frontier Story: A Documentary History of Westward Expansion. Holt, Rinehart and Winston, 1969.
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