Transfer Day in the Virgin Islands
On March 31, 1917, the Danish West Indies were officially transferred to the United States for $25 million. The negotiations began almost 50 years prior during the Civil War when the United States recognized that the islands provided a strategic outpost for the navy (fueling ships and protecting interests in the Panama Canal).
A History of Transfer Day
The St. Croix Landmarks Society posts an interesting and in-depth background of the historical significance of Denmark’s allegiance to the Union during the Civil War
The U. S. Dept of State has archive files covering the Purchase of the Virgin Islands in 1917