The St. Croix River marks a section of the international boundary between the United States and Canada, forming a natural border between the towns on either side of the river bank. This section of the river and the land surrounding it, was fought over heavily by both the French and the English during the 1600s, as both sides believed the river lands should be part of their territory. Later, the river was used as a boundary between the Americas and Canada, and many believed the line between the two countries should be drawn down the middle of the river itself. However, there were still many smaller branches to the river and various islands that were not spoken for, nor could be decidedly belonging to one country or another.