William Edgar Borah was an outspoken Republican United States Senator, one of the best-known figures in Idaho's history. A progressive who served from 1907 until his death in 1940, Borah is often considered an isolationist, because he led the Irreconcilables, senators who would not accept the Treaty of Versailles, Senate ratification of which would have made the U.S. part of the League of Nations.

The history of Idaho is an examination of the human history and social activity within the state of Idaho, one of the United States of America located in the Pacific Northwest area near the west coast of the United States and Canada. Other associated areas include southern Alaska, all of British Columbia, Washington, Oregon, western Montana and northern California and Nevada.