Not to be confused with Savoy, which had a somewhat different history.
These two regions, in what is now France, and formerly were part of the Pays de Gex, being variously under the control of the Swiss, the Genevese and the counts of Savoy. In 1601 they came under the control of France. Their chief feature is that they are geographically isolated from the nearest French territory, and come within the customs domain of Geneva - the customs boundary and the national boundary differ.
In the immediate post WWI period France attempted to advance the customs border to the national one, and the Permanent Court of Justice (predecessor of the International Court of Justice) ruled in favour of maintaining the status quo.
In OTL the matter was resolved peacefully (the area was small, there were historical reasons for their position, and the two countries were at a similar economic level and so there were unlikely to be economic migrants or other issues.
Possibilities in the multiverse:
- The situation escalates, and France and Switzerland are brought into economic and other conflict.
- The open boundary is retained, and is used as a means of "leaving areas of likely damage" to the relative freedom of Switzerland.
Survey of International Affairs 1925 Vol II. C. Macartney & others Royal Institute of International Affairs 1925