To understand this, you basically have to know how and why the Carnation Revolution happened in the first place. This can be put down to quite a few factors but perhaps the biggest are political pressures, economic conditions, and developing mass movements (all of which are obviously related to each other as well).

Following World War II, but especially throughout the 1970s, most of the various colonies throughout the world achieved or were granted independence. This was itself the result of numerous factors, including anti-imperialist movements in colonies and modernising economies. It actually became something of an embarrassment on a global level to have open, unabashed colonies (see, for example, the “diplomatic” granting of independence to Papua New Guinea by Australia which you can read about in Tom O’Lincoln, The Neighbour From Hell). Portugal maintained its colonies well after a lot of other colonial powers had fully committed to decolonisation. Due to this, they suffered embargoes, censure, halted agreements, etc. in the international community. This put massive ideological pressure on the new Popular Power governments that emerged. Furthermore, maintaining the colonies was deeply unpopular among sections of the Portuguese population since it was enormously expensive to maintain.

However, there must have been some reason to hold onto these colonies, right? Well, Angola and Mozambique in particular were rapidly growing economies with cash crops and tourism booming. Meanwhile, Portugal itself was among the least developed (if not THE least developed) in Western Europe. Much of its northern population was still destitute peasantry (Peter Robinson, Portugal 1974-75. Popular Power). Although Portuguese large business owners were rather happy to continue exploitation of the colonies, these profits didn’t exactly feed through to the Portuguese population more generally. This was especially noticeable since most wealth was fed into two massive monopoly corporations, CUF and Champalimaud. Arguments very quickly arose that the government needed to stop wasting money on maintaining the colonies and start looking after its own people. Slogans to this effect were popular among the student movement and even appeared printed on Lisbon bus tickets by radicals in the transport unions (Phil Mailer, Portugal: the Impossible Revolution?).

Finally, all of this links together with the mass movements that were rising up, not only in Portugal but all around the world (most notably in France and Chile). The Carnation Revolution wasn’t just some military coup, it was linked to a mass movement of radical unions, worker councils and student groups. Many of these, especially the student groups, explicitly campaigned for the end of colonisation on moral grounds. Unions also expressed solidarity for anti-colonial struggles which had broken out in Angola, Mozambique and Portuguese Guinea (in part due to their rapidly growing economies). There are accounts from the time of people having conversations in Portuguese cafes and taverns with young people, even as young as eight, who were making coherent political arguments about the evils of colonisation and anti-unionism (Antonio de Figueiredo, Portugal: Fifty Years of Dictatorship).

All of these factors suggest that anti-colonialism was inextricably linked to the broader struggle for democracy within Portugal. After the events of the Carnation Revolution, the new government had little choice but to quickly de-colonise, given the aims of the wave of struggle that had brought them into power, as well as the economic and international political situation they faced.

First I would like to say, that Portugal did not win the Colonial War. In 1974 the were winning in Mozambique (with Rhodesian help), just able to maintain a stalemate in Angola, and losing in Portuguese-Guinea. Losing control over Portuguese-Guinea would have been a major setback as it was the only base in Western Africa where Portuguese ships and planes on their way to Angola and Mozambique could dock/land. Portugal became more and more isolated, especially after the failed coup in Guinea (Operatien Green Sea) and was not able to purchase enough military equipment and the army was generally in poor condition because of financial problems. Marxist revolutionaries in Portuguese-Guinea were equipped by the Soviet Union, had newer and better weapons, and were supported by both neighbouring countries. Furthermore the need of more military personell led to an opening of miltary schools for lower class citizens who were often opposed to Salazar's dictatorship. These new officers were not loyal towards the old elite, often poor and prone to marxist ideas. This led to an development of an opposition within the Portuguese army. In 1974 General de Spinola, who was quite succesful in Portuguese-Guinea between 1968 and 1972, published a book called "Portugal o e Futuro" in which he states, that the Colonial War could not possibly be won. This evaluation was shared by most of Portugal's population and army and led to the widespread support of the Carnation Revolution and the immediate end of the wars. Since the situation in Portugal itself was not stable for several months, a stable decolonization had no priority.
(Source: Alexander Gajewski, Demokratierungsprozesse in Ungarn und Portugal)

Hi, sorry for asking this here but I did not know where to post this question. Does anyone know the title of a documentary about 3 women from the upper-class family living in Portugal around that period? My mom saw the documentary ages ago but she did not catch the title. I tried googling it but to no avail.