Washington is the north-western most state of the contiguous United States. Its northern border lies mostly along the 49th parallel, and then via marine boundaries through the Strait of Georgia, Haro Strait and Strait of Juan de Fuca, with the Canadian province of British Columbia to the north. Washington is bordered by Oregon to the south, with the Columbia River forming the western part and the 46th parallel forming the eastern part of the southern boundary.
To the east, Washington borders Idaho, bounded mostly by the meridian running north from the confluence of the Snake River and Clearwater River (about 116°57' west), except for the southernmost section where the border follows the Snake River. To the west of Washington lies the Pacific Ocean.[5] Washington was a Union territory during the American Civil War, although it never actually participated in the war.