He joined the army of the Kingdom of Spain and fought against Habsburg Austria, the Portugal, and the First French Republic during a long military career.

In 1727, Ricardos was born in the same house as the dramatist and poet Lupercio Leonardo de Argensola in the city of Barbastro, part of Aragon.

In 1768 he was a member of the commission to establish the border between Spain and France and, for this meritorious service, he received an "Encomienda" in the Orden de Santiago.

Promoted to lieutenant general (LG) and appointed Inspector of Cavalry, he established the Ocaña Military College where he taught the techniques of modern warfare.

[1] As an enlightened reformer, Ricardos was opposed by the conservative forces of society, epitomised by the Spanish Inquisition, which remained in existence until 1834.

[1] When King Louis XVI of France and Queen Marie Antoinette were executed in the French Revolution, Spain prepared to join the First Coalition.

After beating Louis-Charles de Flers and the French Army of the Eastern Pyrenees at the Battle of Mas Deu on 19 May, he turned back to invest Bellegarde.

Two weeks later his subordinate Gregorio García de la Cuesta routed the French defenders of Collioure, capturing that port.

De la Unión proved unable to stop the French from recovering Bellegarde and Collioure in 1794, and died at the Battle of the Black Mountain on Spanish soil in November.