The Portuguese Civil War was a conflict that started on September 1890, initiated by the Portuguese Republican rebels in order to establish a Republic of Portugal, facing the Portuguese Royalists that remained faithful to the Kingdom and the Bragança family.
During the reign of Luis I, Portugal had been suffering from a slow decline in power and stability, because of their loss of status in the world and the continuous support of Luis I for the Regeneradores, the main Portuguese Conservative Party. The African Division had, however, legitimized Portugal's control over Angola and Moçambique, which hopefully would, eventually, help Portugal get back on its feet.
However, on July 21st 1889, Luis I suffered a heart attack that left him partially disabled, forcing his son Carlos to become Regent of Portugal. The United Kingdom took advantage of this situation and, on January 1890, they presented an ultimatum: either Portugal ceded a certain region of Africa that connected Angola to Moçambique, and that was coveted by the United Kingdom for their Cape-to-Cairo Railway, or "abide by the consequences", which was pretty much a veiled threat of war. The Portuguese government, unable to make any offer that might be amenable to the British and that allowed Portugal to keep that territory, had no choice but to sign, selling the territory for a paltry sum of money.
While Portugal would soon cut off all ties with the United Kingdom, it was too late, and protests would happen along Portugal. These protests would have the unfortunate consequence of aggravating King Luis I's health, causing him a second heart attack that killed him on August 21st 1890.
Carlos I was crowned a month later, but then several pro-Republican officers and soldiers managed to cut off the new King's ride to his palace after the crowning, intending to kidnap him and his family to force him to renounce to all dynastic rights to the crown, hoping to be able to declare the Republic without bloodshed. However, the Royal Guard prevented them from doing so, and a firefight ensued, in which the Royal Couple died during the crossfire. Troops allied to the Portuguese Republican Party rose up soon, dividing Portugal in two.
The first phase of the war could be said to begin on the same day of King Carlos I's death and end two weeks later. During this phase, troops moved, infighting took place in many cities, and people that supported one side but lived where the other had more power learned to shut up, ran away or died. After these two weeks, a line that crossed from Figueira da Foz in the Atlantic coast to Monte Fidalgo near the border with Spain marked the border between both sides.
The Republicans soon launched an attack towards Porto, the Royalists' provisional capital. Coimbra and Aveiro fell, but an attack towards Maceda was bloodily stopped by the Royalists, who finally managed to halt the Republican offensive. The Republican overstretched supply lines allowed the Royalists to cut the main group of attack from Republican Portugal, and advance towards the south soon started. Slowly but surely, the Royalists managed to recover all lost ground, and they would also manage take Republican territory in a series of daring operations, among them the takeover of Marinha Grande and Leiria, carried out by the First Royal Army by landing troops near the cities.
In April, Lisbon and the surrounding lands were isolated from the rest of Portugal, preventing the Republican troops in Southern Portugal from receiving supplies produced in Lisbon's factories and easing their fall to the Royalists in less than two months.
The main final act of the war was the assault on Lisbon, which had been postponed several times in fear that Carlos I's children would be killed in retaliation, a thorny affair given that the elder, Luis Filipe, was the yet-to-be-crowned King of Portugal. The assault took place on July 21st, and was a decisive victory for the Royalist troops, who, however, where unable to reach all of their objectives, because Luis Filipe and his younger brother, Manuel, had died of pneumonia around April. However, war would not officially end until Goa, which had fallen to the Republicans early in the war, was taken back in August 24th 1891.
Most nations were supportive of the Royalist faction. Spain was one of the most outspoken supporters, selling them weapons at low cost, hosting the Regent and collaborating in the blockade of Republican Portugal. Germany and Brazil followed suit in their support for the Royalists. France and most American nations decided to remain neutral in the issue of the war, while the United Kingdom, considered by many the nation that had caused the war to begin, tried to mediate between the two factions, but they could not meet with the Republicans and the Royalists ignored them.
The end of the war brought relief to the people of Portugal. Reconstruction of the infrastructure lost in the fighting, as well as most buildings, was initiated soon, and Afonso was crowned King. Spain became a support for Portugal, helping them rebuild and being taken as an example on how to structure a democratic government.
However, this was not the end of the problems, because King Afonso was killed in November 1891 by a supporter of the Republican party that intended to avenge the deaths of his party companions. This eventually lead to the unification of Spain and Portugal in the United Empire of the Spains.