[10] Having changed its name in 1943, the PCI became the second largest political party of Italy after World War II,[11] attracting the support of about a third of the vote share during the 1970s.

Apart from the 1944–1947 years and occasional external support to the organic centre-left (1960s–1970s), which included the PSI, the PCI always remained at the opposition in the Italian Parliament, with more accommodation as part of the Historic Compromise of the 1970s, which ended in 1980, until its dissolution in 1991, not without controversy and much debate among its members.

[17][18] Under the leadership of Enrico Berlinguer and the influence of the miglioristi in the 1970s and 1980s,[19] Marxism–Leninism was removed from the party statute[20] and the PCI adhered to the Eurocommunist[21] trend, seeking independence from the Soviet Union[22] and moving into a democratic socialist direction.

The official program, drawn up in ten points, began with the intrinsically catastrophic nature of the capitalist system and terminated with the extinction of the state.

For a while, this identity resisted, but the fast progress of the reaction in Europe produced a change of tactics in a democratic direction within the Bolshevik party and consequently within the Comintern.

This allowed the intense activity of the Communist International to deprive the party's left-wing of authority and give control to the minority centre which had aligned with Moscow.

Before the Lyon Congress in 1926, the Centre won almost all the votes in the absence of much of the Left, who were unable to attend as a result of fascist controls and lack of Comintern support.

After Joseph Stalin dissolved the Communist International in 1943, the exiled members of the PCd'I in Moscow changed the party's name to the PCI on 15 May.

They were well prepared for clandestine activity because of the structure of their organisation, and the fact that they had been victims of systematic repression by the authorities; more than three quarters of the political prisoners between 1926 and 1943 were communists.

Throughout the dictatorship, the party was able to maintain and feed a clandestine network, distribute propaganda leaflets and newspapers, and infiltrate fascist unions and youth organisations.

[27] The party and communist partisans, among others, then went on to play a major role in the resistance movement that led to the fall of the Fascist regime in Italy.

Alcide De Gasperi, the DC leader and prime minister of Italy, was losing popularity, and feared that the leftist coalition would take power.

While the PCI was growing particularly fast due to its organising efforts supporting sharecroppers in Sicily, Tuscany, and Umbria, movements that were also bolstered by the reforms of Fausto Gullo, the Italian Minister of Agriculture.

[37] On 1 May, the nation was thrown into crisis by the Portella della Ginestra massacre, in which eleven leftist peasants (including four children) were murdered at an International Workers' Day parade in Palermo by Salvatore Giuliano and his gang.

The United States government provided support to anti-PCI groups in the election,[41] and argued that should the PCI win, the Marshall Plan and other aids could be terminated.

It spent $10–20 million on anti-communist propaganda and other covert operations, much of it through the Economic Cooperation Administration of the Marshall Plan, and then laundered through individual banks.

[42] Fearful of the possible FDP's electoral victory, the British and American governments also undermined their campaign for legal justice by tolerating the efforts made by Italy's top authorities to prevent any of the alleged Italian war criminals from being extradited and taken to court.

[47] The party leadership, including Palmiro Togliatti and Giorgio Napolitano (who in 2006 became President of Italy), regarded the Hungarian insurgents as counter-revolutionaries as reported at the time in l'Unità, the official PCI newspaper.

[52] Although the PCI relied on Soviet financial assistance more than any other Communist party supported by Moscow, declassified information shows this to be exaggerated.

From 1967 through 1973, PCI members were sent to East Germany and Moscow to receive training in clandestine warfare and information gathering techniques by both the Stasi and the KGB.

Shortly before the 1972 Italian general election, Longo personally wrote to Leonid Brezhnev asking for and receiving an additional $5.7 million in funding.

According to Mitrokhin, the party asked the Soviets to pressure the StB, Czechoslovakia's State Security, to withdraw their support to the group, which Moscow was unable or unwilling to do.

[55][56] A third of the PCI membership, led by Armando Cossutta, refused to join the PDS, and instead seceded to form the Communist Refoundation Party.

Amongst other measures, the local PCI administration tackled urban problems with successful programmes of health for the elderly, nursery education and traffic reform,[58] while also undertaking initiatives in housing and school meal provisions.

Health care improved substantially, street lighting was installed, new drains and municipal launderettes were built and 8,000 children received subsidised school meals.

In 1972, the then-mayor of Bologna, Renato Zangheri, introduced a new and innovative traffic plan with strict limitations for private vehicles and a renewed concentration on cheap public transport.

The city centre was restored, centres for the mentally sick were instituted to help those who had been released from recently closed psychiatric hospitals, handicapped persons were offered training and found suitable jobs, afternoon activities for schoolchildren were made less mindless than the traditional doposcuola (after-school activities), and school programming for the whole day helped working parents.