15 January On the eve of the congress, the leadership’s report on the period since the Bologna Congress was distributed. It highlighted the substantial growth achieved: the PSI, which in 1919 had 1,891 sections with 81,464 members, now had 4,367 sections and 216,327 members. This increase was also seen in terms of deputies elected to parliamentary (from 47 to 156) and local government (350 municipalities and 8 provinces at the time of the XVI Congress, 2,500 municipalities and 25 provinces in January 1921). After the final meetings of the fractions were held on the morning of January 15, the congress was opened at 14:00 by the provisional president
Giovanni Bacci, who recalled the anniversary of the Spartacist insurrection of 1919. according to the Kabakchiev, this split between revolutionary and non-revolutionary forces, which had already occurred in many countries, was also necessary in Italy so that the whole European continent was ready for the final upheaval which would have led to peace and the solution of the problems of unemployment and misery caused by bourgeois policies. Nicola Bombacci spoke of a painful but necessary separation, in the light of the revolutionary period the country was going through and the need for clarity within the socialist movement and its “two schools”. Anselmo Marabini then intervened, from the "circular" fraction, explaining that his own group would vote for "the motion that will be recognized by the representatives of the third international", accusing the unitaries of dividing the party in the name of unity. It was evident that any hope of avoiding the rupture had by now waned, as Graziadei and Paul Levi had become aware. Up until the day before they had tried to mediate with Serrati to obtain the expulsion of the reformists and the unity of the rest of the party, however they were stopped by the delegates of the Comintern: Rákosi would later report that he had telegraphed to Moscow to request new directives on the matter, obtaining in response the authorization to continue along the path of forcing the split.
20 January Then came the sixth day of the congress, during which the voting was scheduled. First, however, there was room for other interventions, such as that of
Jules Humbert-Droz who, as
Rosa Bloch had previously done, spoke of the imminent split of the communists from the Swiss Socialist Party and hoped that the Italian Socialist Party, who had been an example during and after the war, did not turn its back on the Third International; and that of Costantino Lazzari, who declared that he was withdrawing his motion to adhere to the unitary one. Then Kabakchiev spoke and was peremptory in affirming that the factions that did not vote for the expulsion of the reformists would in turn be expelled from the International. After half an hour of controversy and incidents, Misiano read a joint statement by Kabakchiev and Rákosi, according to which the only acceptable motion was the communist one.
The exit of the Communists Following the withdrawal of the motions from the circular and intransigent fractions, voting proceeded on three motions: the unitary or "Florence" one (signed by Baratono and Serrati), the communist or "Imola" one (Bordiga-Terracini) and the concentrationist or "Reggio Emilia" one (Baldesi-D'Aragona). President Bacci gave an account of the results on the morning of 21 January: out of 172 487 valid votes, 98,028 went to the Unitarians, 58,783 to the Communists and 14,695 to the concentrationists, with 981 abstentions. The announcement of the vote was followed by an intervention from Polano (the Youth Federation "resolves to follow the decisions that the communist fraction will take") and by Bordiga's announcement that the majority of the congress had placed itself outside the Third International, and therefore the delegates supporting the communist motion would leave the hall. Soon after the communists walked out of the Teatro Goldoni singing
The Internationale and gathered at the
:it:Teatro San Marco. There, they held the
I Congress of the Communist Party of Italy and ratified the birth of the new party, into which a few days later, as announced, the youth organization also merged.
Other business The remaining majority delegates in the PSI congress continued their work. A motion signed by Paolo Bentivoglio was unanimously approved in which the PSI's adhesion to the Communist International was reiterated «accepting its principles and method without reserve», and protesting against the declaration of exclusion issued by the representative of the Executive Committee. The hope was that at the next congress of the Comintern the dispute could be resolved by blaming Kabakchiev for having gone beyond the limits of his mandate. A speech by Adelchi Baratono followed, highlighting the differences between the unitary motion and the concentrationist one, and urging the right wing to accept the revolutionary program of the party and the principles of the International. Turati then intervened, urging a common effort for "the Party to become the class and become the great union of the national and international proletariat"... His words did not reassure everyone, and there were those who judged them "elastic" and "such as not to be relied upon", to which Serrati replied that he would be vigilant "on our comrades of the right wing" and that, if they behaved in a way harmful for the party «one cannot have mercy on them». In the course of the morning the new committee of the PSI was also elected, which turned out to be composed exclusively of unitaries. Two parliamentary deputies were on the list of candidates drawn up by the majority fraction:
Gaetano Pilati, as representative of the proletarian League of the maimed and war veterans, and
Giovanni Bacci, as chairman of
Avanti! who resided in Rome, where he could easily work in the headquarters. The proposal was opposed by Giuseppe Romita, who maintained that being a member of the Directorate was incompatible with being a holder of public office, but nevertheless the assembly approved the list by a large majority. In addition to Pilati and Bacci, the new committee comprised Serrati (who was also confirmed as chairman of
Avanti!), Baratono, Sebastiano Bonfiglio, Franco Clerici, Domenico Fioritto, Giuseppe Mantica, Giuseppe Parpagnoli, Giuseppe Passigli, Alojz Štolfa, Emilio Zannerini, Raffaele Montanari and Eugenio Mortara. The work of the congress closed at 13:00, after President Bacci had exhorted his comrades to resume work immediately "in the Sections, in the Party, in the country, in the International" and after the delegates who had praised the Russian Revolution and sung
The Internationale and the
Bandiera Rossa. ==Reactions and consequences==