The acquisition of the Danish West Indies by the United States was formalized through a treaty on March 31, 1917. This transfer of ownership marked an important point in U.S. territorial expansion in the Caribbean. Amidst the context of World War I, American officials were keen to secure strategic locations that could support military and naval operations within the region. The U.S. recognized the islands' significance given their proximity to both the Panama Canal and the Caribbean Sea, vital for both defense and trade routes. The formal negotiations began in 1916, culminating in an agreement where Denmark received $25 million in gold for the islands, which included Saint Thomas, Saint John, and Saint Croix.

Despite earlier offers as far back as the 1860s, which had been declined by Denmark, the escalating global tensions and the U.S. interest in a stronger presence in the Caribbean made this acquisition feasible. The treaty was ratified by the U.S. Senate and subsequently by the Danish parliament, paving the way for the transfer of the islands. On March 31, 1917, the islands officially became American possessions and were renamed the U.S. Virgin Islands. This transition process involved a relatively smooth handover and integration into the U.S. governance framework.

The U.S. Virgin Islands would later serve strategic military roles, especially during World War II, further solidifying the necessity of their acquisition. It also marked a continued shift in U.S. foreign policy towards increased intervention and presence in the Caribbean, influencing future relations with various island nations and communities in the area. The islands remained a point of interest not only for their geography but also for cultural ties and resources, impacting U.S. expansionism throughout the 20th century.