Final answer:
The scenario of Guadeloupe switching sides in the war and becoming friends with the United States best exemplifies the cause of Alliances in World War I.
Step-by-step explanation:
The scenario where the island of Guadeloupe switches sides in the war and becomes friends with the United States best fits under the cause of Alliances in World War I. Alliances were agreements between countries to provide military support and defend each other in the event of an attack. In this scenario, Guadeloupe switched sides and formed a new alliance with the United States, indicating a shift in their allegiances. It is important to note that Alliances were one of the main causes of World War I, as they created a web of obligations that pulled multiple countries into the conflict.