Despite the fact that the island is one of the smallest islands in the World that is divided between two nations, the border is not really that strange. It is generally split in half with the French getting the half to the North and the Dutch taking the part to the South. What is strange is that the border does not divide the island evenly and we only have a folklore story as to why. France clearly got the better part of the deal.
There are several stories as to how the island was divided. The one that local legend seems to favor is that two sailors, one French, the other Dutch were asked to start at the same point and walk the coastline in opposite directions. Where they met again would determine the halfway point and thus how to divide the island. Some stories say that the Dutch sailor got drunk on rum or “Jenever (Dutch Gin) and walked too slow. Others say that the French sailor cheated by running or cutting corners. Neither story accounts for the fact that border does not go straight across the island. A ridge line would explain some of the strangeness but not all of it.
The other strange part of the island is the number of times occupation of the island changed after the Treaty of Concordia supposedly settled the issue once and for all. Between 1648 when the treat was signed and 1816, the occupation of the island switch between being all French, all British or all Dutch ten times. The shortest period of occupation was in 1781 when the British held the island for just ten months.