What does the phrase from sea to shining mean?

From sea to shining sea" is a poetic phrase that refers to the width of the United States, stretching from the Atlantic Ocean to the Pacific Ocean. It is often used in patriotic contexts to express the nation's vastness and unity. The phrase is believed to have originated in the 19th century and was popularized by a song written in 1861, shortly after the start of the American Civil War. The song, "The Battle Cry of Freedom," contains the line "From sea to shining sea, / The Union must and shall be free." Since then, the phrase has been used by political leaders and artists alike to evoke the image of a unified nation stretching from coast to coast.