Which French King transferred control of the territory west of the Mississippi to King Carlos III of Spain?

The transfer of control of the territory west of the Mississippi from France to Spain was carried out by King Louis XV. This event occurred in the context of the Treaty of Fontainebleau in 1762, which was a secret agreement made during the Seven Years' War. As a result of the treaty, France ceded this vast territory to Spain to compensate for Spain's loss of Florida to Britain, essentially reshaping the geopolitical landscape of North America at that time.

Understanding the significance of this transfer is important for contextualizing the colonial history of North America, particularly in relation to the influence of European powers in the region. The other options—Louis XVI, Charles IX, and Henry IV—were either not in power during the time of this transfer or were involved in different historical contexts that do not pertain to this specific territorial change. Louis XVI, for example, ruled later and faced different political challenges, while Charles IX and Henry IV were earlier monarchs whose reigns were focused on different issues in France.