How did the Bourbons acquire the duchy of Parma?

The House of Bourbon acquired the Duchy of Parma and Piacenza through inheritance and subsequent diplomatic treaties.

In 1731, the duchy passed to the Spanish Bourbons upon the extinction of the Farnese family. The first Bourbon duke was Don Carlos (the future Charles III), who claimed the territory by right of his mother, the heiress of the last Farnese dukes.12

Although Don Carlos later renounced Parma to secure international recognition as the king of Naples-Sicily, the duchy was eventually secured for his brother, Philip (Don Felipe), under the Treaty of Aix-la-Chapelle in 1748. Following the Napoleonic period, during which the duchy was annexed to France and later assigned to Marie-Louise, the Congress of Vienna and the subsequent Treaty of Paris of 1817 ensured that Parma would revert to the Bourbons upon Marie-Louise's death, which occurred in 1847.12