Extract from "Socialism in Spain: A historical analysis" by Josep Munté
As a general rule of the thumb, it is the far left of politics which is more disorganized than its more moderate, social-democratic counterparts on the centre-left. Curiously, and despite the disappearance of many of the various left-wing parties that had existed prior to the elections of 1977 and 1979, which consolidated the party system, at the regional level, the so-called sopa de letras of social-democratic parties continued. That is not to say that there weren't divisions within the Communist camp. To the left of the PCE existed various Maoist parties, such as ORTE or the PTE, which claimed to represent true communism and called for a cultural revolution in the idealised manner present in many parties of this kind at the time. (1) Furthermore, after the struggles within the PCE's main factions (carrillistas, afganos and leninistas), the so-called afganos (2) would form their own splinter party, the PCPE.
At the national level, only Tierno Galvan's FPS, Felipe González's PS and Rodolfo Llopis's PSOE were represented in Parliament in 1977, and by 1979, Llopis had lost his seat, and hence the historical party of the moderate left vanished from the national parliamentary left, although it would retain representation at the municipal and at the regional level in the Basque Country until its merger with the PCE. The other two main forces after 1979 were the PS, which could be considered as the more relatively more right-wing of the two, and hence more likely to establish bridges with the social democrats within the UCD and the FPS, which stood somewhere in between the UCD and the PCE, and which, for instance managed to reconcile governing locally with the PCE with supporting the UCD governments after 1987 election, although on this it was quite helpful the good relationship between the UCD's Pedro Solbes and José Bono from the FPS.
The more problematic situation presented itself, instead, at the regional level and in particular in Catalonia, where the left-wing opposition had been quite strong and where Catalanism and left-wing politics did not necessary ran in parallel, like in Galicia, nor against each other, like in the Basque Country, but rather were intertwined in a complex network of small parties. For instance, before the 1980 election, beyond the PSUC (which also had both Catalanist and anti-Catalanist members), there was a myriad of Catalanist and non-Catalanist (or even anti-Catalanist, like the PSA) centre-left parties. It would perhaps be most interesting to name a few, to put things in perspective. Besides the PS's Catalan Federation, there was Convergència Socialista de Catalunya (itself the result of the merger between the original CSC, alongside the PPC, the PSC-ex-Reagrupament and some socialist ERC members), the PSA, the PSC-Reagrupament (later on Moviment Socialista de Catalunya) and ERC. To some degree this differences between the parties were reduced, especially after the merger of PSA with the PS' Catalan federation, but they seemed most important given the very reduced electoral space that social democracy had in Catalonia, where the Communists were, even moreso than in the rest of Spain, the hegemonic party on the left. However, by 1980, the consolidation that took place across Spain also affected Catalonia: The CSC and parts of the PSC-R, led by Joan Reventós would become a part of the PSP-led Federación de Partidos Socialistas. The MSC (previously PSC-R) would disperse, divided in its loyalties and some members would join CiU, ERC, the PS or the CSC. As a result, on the occasion of the first regional elections since 1934, the left-wing was composed of (in order from least to most Catalanist) PS-PSA, PSUC, CSC and ERC.
In the Basque Country, the divisions were deeper and certainly more dramatic, as they took place under the watchful eye of ETA and the conflict in the region that pitted the Government, ETA and a series of far-right groups, that were probably helped by elements within the police and the Armed Forces. Charcteristic of this time was the political violence of ETA against civil figures, such as Jaime Mayor Oreja, and leader of the UCD in Guipúzcoa at the time, who was almost killed by ETA (3). Besides the PCE, quite weak in the region and suffering from a rift between Basquists (Roberto Lertxundi) and non-Basquists (Ramón Ormazabal), there were EE (4) (associated with ETApm), HASI (associated with ETAm) (5), the PSE and the PSOE. Alongside them, there was a large number of minor parties of the Basque radical left type (6), that together with HASI (after the expulsion of more moderate members) would go to form Herri Batasuna, which to this day remains the main force of the Basquist left.
The PCE and the PSE would fight for the same electorate, the non-Basque-speaking, usually of immigrant background industrial worker in the large industrial towns or cities of the Basque Country, and particularly of Biscay. EE would however find itself in a more complicated position, trying to walk the thin line between HB and the non-Basquist parties, as an option of moderate left-wing Basque nationalism. As it turned out, although the party was relatively successful given the circumstances of political polarisation present in the Basque Country, the party would end up merging with the renamed PCE in 1992 to form the new post-communist outfit in the region.
In Galicia, a similar story took place. Besides the PCG, quite weak in the region and the PS' federation, there was a series of parties that brought together social democracy (like the PSG) or more radical socialism (such as UPG and ANPG) and Galician nationalism. One strange particularity of this mixture of nationalism and left-wing politics was the strength of Maoist parties in Galicia, which manage to win one seat in the 1981 regional election, one of the rare occasions in which a party to the left of the PCE ever managed to win representation. That is not to say that Galician nationalism was the patrimony of the left, as "Galicianism" was also a core component of the centrist-nationalist Partido Galeguista and of the autonomist factions of the UCD, Galicia's undisputable party of power.
In Valencia, where the conflict between pan-Catalanist Valencian nationalism and anti-Catalan Valencian regionalism was a key feature of the bitter political struggle (7) between the PCE, siding with the former intellectual current and the UCD, siding with the former alongside minor right-wing groups such as Unió Regional Valenciana, there was also a large number of small parties that sided with the Fusterian (pan-Catalan) side of the identity conflict, and which gravitated closer to the thesis of the PCPV and which would later merge into the Partit Socialista del País Valencià, which would form a core part of Tierno Galván's FPS. However, not all the forces merged into the PSPV, with a few, more nationalist than social-democrat forces forming Unitat del Poble Valencià in 1981, a relatively important political player (8) in the post-Cold War politics of the Valencian region.
Notes: (
1) That is to say, that they had no freaking idea of what was going in Mao's China, and rather relied on a disturbingly utopian vision of it.
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2) I'll allow the readers of the TLIAWOS to figure out why a pro-Moscow section of the PCE was nicknamed "the Afghans".
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3) OTL. Mayor Oreja, who was the nephew of Foreign Affairs Minister, Marcelino Oreja, was almost killed by ETA in 1980. The story is a fun one: ETA throws grenade at his office from a car, the grenade hits a street light and bounces into the air, where it explodes without even hurting him. And that's how basebomb was created

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4) Euzkadiko Ezkerra. OTL it would later merge with the PSE to form the PSE-EE of our days.
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5) Herri Alderdi Sozialista Iraultzailea. HASI means '(to) begin' in Basque. They were the nastier of the two, as befits the group associated with the nastier of the two ETA groups.
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6) The term
abertzale will not become as popular TTL as it has OTL. Terms like
zulo though...
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7) And by bitter, we mean 'bombing stuff'. See:
Batalla de Valencia
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8) Sort of a centrist URV.