If Alfonso XII lives as many years as his mother (Isabella II died at 73 years and a half), he had lived 45 years longer (he had died in 1930, and not when he OTL died, to three days before his 28th birthday), which could contribute to numerous changes in world history:
- The Restauration system had gradually transformed Spain into a genuine parliamentary monarchy (the Spanish Constitution of 1876 states that the Spanish sovereignty was staying at the King and the Cortes), as occurs in both Belgium and the United Kingdom.
- The Spanish-American War would have been avoided because he would be the representative of the Spanish royals making the transatlantic journey through the 4th Centenary of the discovery of America (instead OTL, where his little sister, the Infanta Eulalia, who after the trip warned the Spanish government of the need to establish a autonomy to Cuba, Puerto Rico and the Philippines in order to avoid an independence rebellion that would be used by the United States), and seeing the social situation of the Spanish Antilles, he strongly support creating an autonomous status for Cuba, Puerto Rico and the Philippines to establish a broad self-government within their stay in the Kingdom of Spain, moving away the possibility of an US intervention occurred.
- Regarding his position in foreign policy:
- In Europe, Alfonso XII was a great germanophile. In a banquet held in Germany where he met with other European monarchs, including the Kaiser William I, Alfonso XII committed to a personal alliance with Germany (an alliance in the style of the League of the Three Emperors), compromising the presence of half a million Spanish soldiers at the French border before any Franco-German conflict. Therefore, if he had been the Spanish king during the WW1, he had shown favor to intervene against France for Germany, possibly generating many problems to Entente powers (the creation of a new line of battle in the Pyrenees and a highly probable closure of the Strait of Gibraltar) and trying to get alliance with Italy if it accepts what the Austro-Hungarian Empire is willing to cede (forced by Germany and Spain) and possible Italian conquests on territories controlled by the Entente (Corsica, Nice, Savoy, Malta and Tunisia).
- In America, he could have gotten the various Latin American republics were more favourable to Spanish investments entry (especially after his trip to America), trying to be the arbiter between territorial disputes, trying to start a PanHispanic speech to avoid Anglo-US interferences in Latin America, etcetera.
- In Spanish colonial policy, he would surely have supported the Spanish conquest of the Rif and the proclamation of a Spanish protectorate over the rest of Morocco, taking advantage of the First Melillan campaign, occured in OTL 1893. It would also have avoided the territorial deliveries to France in probable territories of Spanish colonization, as were Mauritania and an expansion of Spanish Guinea, occurred just before the Berlin Conference (this happened mainly because French had many interests in Spanish economy and they bribed some Spanish leaders and potentates for Spain leave many legitimate territorial claims on Africa).
- And in view of his admiration for the German Empire, it would not be surprising if he try something similar, creating a new Spanish/Iberian Empire in which the Kingdom of Portugal is included, especially after the humiliating 1890 British Ultimatum suffered by Portugal following the colonization of Rhodesia, especially if the Portuguese political crisis degenerate into an openly republican revolt, as happened in OTL 1891 or as in an AH created by Milarqui. And without forgetting, that he would seek to copy in Spain the laws on labor and social security created by Bismarck to stop Marxism in the working environments, and a deep education reform to eradicate illiteracy in Spain and would improve Spanish science, technology and culture.
- Finally, he would strongly recommend that the Spanish government gave the total financial support to enormous technological projects invented in Spain, as the electric submarine invented by Isaac Peral and inventions made by Leonardo Torres Quevedo, greatly strengthening the industrial and military capacity of Spain.
All these changes would prevent the terrible Spanish Civil War of 1936-1939 occur because Alfonso XIII (or Fernando VIII, who apparently was the name Alfonso XII wanted for his firstborn son, according to some forum members) would be an unique witness to the political management of his father, thus avoiding huge mistakes he made during his OTL reign, and keep Spain as a key player on the international scene while a healthy parliamentary system developed in Spain.
What do you think?
PS: However, the best scenario for Spain, concerning Alfonso XII, is that the revolution that overthrew his inept mother in September 1868, had placed him on the Spanish throne, and the period known as the Revolutionary Sexennium would have been a Regency on behalf little Alfonso XII, who had been in the hands of General Serrano, the general Espartero and/or the Duke of Montpensier (he was uncle of Alfonso XII and his future father-in law, as he was the father of Maria de las Mercedes de Orleans), with General Prim as head of Spanish government.
In that way, it would not have produced the enormous political and social crisis occurred in those years, avoiding the 3rd Carlist War and the Cantonal Uprising and initially quell the Cuban rebellion of October 1868 in its beginnings, as occured in the OTL Puerto Rican rebellion of September 1868.
PS2: My previous post had some typos.