Every Portuguese person knows what happened on the 25th of April 1974. The Revolução dos Cravos (Carnation Revolution) was the pivotal event in creating a modern Portugal, and the nation we know today. In fact, the date is so widely known that the phrase 'Revolução dos Cravos" isn't widely used. Much in the same way Americans refer to the 4th of July, the Portuguese speak of the 25th of April.
What happened on that day?
The short answer is a military coup. It was organized by an armed forces group known simply as the MFA (Movimento das Forças Armadas, or Armed Forces Movement), which encompassed a wide range of political views and ideas for the future of the country, but was united in its aim of ending the authoritarian Estado Novo (New State) regime. The MFA secretly commandeered both a significant part of the country's military apparatus and had a plan. On the 24th of April, a song was to be played on the radio by DJs friendly to the coup. It was Portugal's 1974 entry in the Eurovision Song Contest, Paulo de Carvalho's E Depois do Adeus. This would signal the military to start prepping for the following day. On the 25th of April, at 12:20 am, a different song would play. Grândola Vila Morena by Zeca Afonso would signal that key military and civilian targets were to be taken at the same time. The plan worked brilliantly, and the far-right regime's authorities were none the wiser until it was too late. The revolution happened with almost no blood spilled. Only four people were killed on that day, and those two songs would be forever remembered in Portugal as songs of freedom.
Despite the military urging the population to stay home over the radio, thousands of people took to the streets in Lisbon to celebrate with the troops. One of the central gathering points was the Lisbon flower market, and carnations were in season. Many of the insurgents put carnations on the barrels of their guns, to symbolize the fact that they hadn't had to shoot them. These images were broadcast around the world and become synonymous with one of the most peaceful revolutions in the world.
What brought it on?
Portugal and Spain, having remained neutral in the Second World War, were some of the very few countries in Europe to still have authoritarian far-right regimes in power at this point in history. Portugal's original fascist dictator, António de Oliveira Salazar, the strongman who had engineered the Estado Novo, had already passed away. His replacement, Marcello Caetano, didn't have the same aura of invincibility. The socially conservative and economically austere politics of the Estado Novo were making the regime progressively more unpopular as Europe recovered from the great war and started heading into the future. Furthermore, the regime strongly resisted decolonization, dragging Portugal into a massive, bloody, horrifying series of conflicts in Africa to keep its stranglehold over Angola, Mozambique, Guinea Bissau, São Tomé and Príncipe and Cape Verde. The war had been raging for over a decade and had already killed almost 10.000 Portuguese soldiers. The military had just about had enough, and so had the people.
What happened afterwards?
As we mentioned, the MFA was quite diverse ideologically. Its leaders ranged all the way from communists, who wanted Portugal to enter the USSR's orbit to free-market capitalists, who wanted to make Portugal a liberal democracy. When the regime fell, every political prisoner was released, and every politician who was in exile returned to the country. Some of the greatest political minds in Portugal's history, such as Álvaro Cunhal, Mário Soares or Francisco de Sá Carneiro entered the political fray and the PREC began. The PREC (Período Revolucionário em Curso or Ongoing Revolutionary Period) would go on for two years, with political parties forming and disbanding, much confusion, and several attempted coups and reactionary initiatives.
One year after the revolution, on the 25th of April 1975, elections were held for an assembly that would draft the Portuguese constitution. That summer, known as the Verão Quente (Hot Summer) was perhaps the tensest moment of the whole process. Several different currents were trying to reach power. The constitution was finally approved on the 2nd of April 1976. The elections held on the 25th of April of that year were the first free elections for the Assembly of the Republic, marking the beginning of a democratic and finally free Portugal.