The Iberian Union was formed in the wake of the Spanish-Portuguese War of 1915 in which the Spanish successfully ended the Portguese Revolution by driving the Republicans from the mainland and off into the Azores where they became protected by the United States. The Spanish, instead of withdawing from Portugal declared a new Iberian Union on December 20, 1915 and the signing of the Treaty of Lisbon with the Protuguese Republicans (represented now within the United States) which officially created the Iberian Union on the same day as the treaty.
Alfonso XIII's son, Alfonso, died when he contracted influenza and died suddenly. His next son, Jaime, ascended to the throne on April 14, 1927 when his father died from throat cancer. He became King Jaime IV on the same day at the age of 19.
As King he continued to claim the throne of France as well as Spain, but that did not get him far with the French. He was then coronated in Madrid as the King of Spain, King of Portugal, and the Emperor of Iberia.