Short answers, pulled from the story.
The Kingdom of Portugal is traditionally considered to have been founded on the 5th of October 1143, when Alfonso VII of León and Castile recognized Afonso Henriques as king through the Treaty of Zamora. An earlier date, the 26th of July 1139, marks when Afonso Henriques was acclaimed king by his troops after the Battle of Ourique. Papal recognition followed in 1179 with the bull Manifestis Probatum.
The monarchy collapsed with the 5th of October 1910 revolution, which drove King Manuel II into exile in the United Kingdom and established the First Portuguese Republic. Contributing factors included the 1890 British Ultimatum, which forced Portugal to abandon its African expansion and damaged the monarchy's prestige, and the Lisbon Regicide of the 1st of February 1908, which boosted republican support.
Vímara Peres, a vassal of the King of Asturias, established the County of Portugal in the 9th century as part of the Reconquista. The county later became part of the Kingdom of León in 1097 before evolving into an independent kingdom in the 12th century.
The 1890 British Ultimatum forced Portugal to halt its territorial expansion in Africa. The ultimatum damaged the monarchy's domestic prestige and strengthened republican political movements, contributing to the eventual collapse of the monarchy in 1910.
From 1580 to 1640, the Kingdom of Portugal was in personal union with Habsburg Spain, meaning a single monarch ruled both crowns without formally merging the two kingdoms. The union ended after the Portuguese Restoration War of 1640-1668.
The Portuguese Empire ended definitively with the handover of Macau to China in 1999. Earlier milestones included the independence of Angola and Mozambique in 1975, and the independence of Brazil, which preceded all of these by well over a century.