Confused former national romantics – nationalistically oriented in their views and convictions on the question of national unification, children from the prewar [Nationalist] Yugoslav Youth who were perishing as guerrillas on Balkan battlefronts, wild individuals of social-revolutionary orientation who saw no difference between anarchist terror and the mass movement, the rebels of Odessa, anarcho-individualistic literati, old Serbian routineer politicians whose ambitions were disproportionately greater than their subjective capabilities... new dissidents of Yugoslav [Nationalist] Youth who were leaving terroristic royalist organizations, a fair number of university trabants from various political groups, and very few proletarians – manual workers, those were the elements that made up the first phalanx of our leftist movement.Miroslav Krlezha, 1935
It might seem odd that the members of Yugoslavia's early Communist movement should be grouped alongside the opponents of centralism and unitarism, the Communists being among the most eager supporters of those policies. Nevertheless, no group seethed in greater agitation against the post-1918 Yugoslav system than the Communists, and its large following was mainly among the nationally disaffected.
The history of indigenous communism in Yugoslavia during the first years of the first Yugoslav state is one of great strides and sharp reversals.  The Unification Congress of the Komunisticka partija Jugoslavije (KPJ, Communist Party of Yugoslavia), or of the Socijalisticka radnicka partija Jugoslavije (komunista) (SRPJ[k], Socialist Workers' Party of Yugoslavia [Communist]), as the party was called until June 1920, marked the end of the first phase in the consolidation of the Comintern's South Slavic section. Despite its considerable successes, the KPJ was not destined to become a compact entity during its two years of legality. As a result of being forced underground in 1 92 I, the party was decimated. In the next decade and a half, though it increasingly bent to the requirements of Moscow, it was at the same time weakened internally by factionalism. Thus, though it was saddled with the ballast of Russism (less a discredit in Yugoslavia than in the other East European countries), it did not, until Tito's advent in 1937, have anything like the discipline of the Moscow central party.
The KPJ itself was an uneasy combination of independent leftists, many
of them, at least in the former Austro-Hungarian territories, from the
ranks of the Nationalist Youth, and of Social Democratic groups, whose
various traditions and stands on the national question were discussed in
Part II. At the Unification Congress (Belgrade, April 20 – 23, 1919) the
party was clearly under the great influence of Srpska socijaldemokratska
partija (SSDP, Serbian Social Democratic Party), which joined the new Communist
movement en masse and gave it a direction that was wedded to certain orthodox
– but not quite Bolshevik – traditions of old Serbian Social Democracy.
The centrist faction, at equal distance from the Communist left and the
reformist traditions of Social Democracy, was defeated at the Second Congress
(Vukovar, June 20 – 24, 1920), at which point the party largely assumed
its familiar ideological contours. Most of its energies were devoted to
militant trade-union action, the peasant and national questions being largely
ignored. Nevertheless, at the elections for the Constituent Assembly in
1920, the KPJ gained 198,736 votes, or fifty-nine seats, ranking fourth,
after the ruling Democratic and Radical parties and the oppositional HPSS,
in ballots cast.
Most of the Communist votes (see map 3-4) came from Montenegro, Macedonia, Kosovo, and Metohia, the showing in Montenegro being most impressive (37.99 percent of the ballots cast). But in the more industrialized areas, such as Slovenia and Croatia-Slavonia, the KPJ polled 10.29 and 7.13 percent, respectively, below its statewide average of 12.34 percent. Its performance was not exceptional in the major industrial cities (Osijek, 26.73 percent; Zagreb, 24.64; Ljubljana, 17.04; Maribor, 14.03; Sisak, 13.52; Varazhdin, 10.54; Celje, 0.75), though it did very well in some other urban centers (Split, 35.7 percent; Subotica, 34.62; Belgrade, 32.25) and overwhelmed certain industrial zones (the Trbovlje mining region in Slovenia, 66.42 percent). On the whole, however, the KPJ's successes cannot be accounted far in terms either of the base that the Communists appealed to or class orientation. In Macedonia and Montenegro, where the KPJ had its most impressive successes, there were no organized national parties that could wage legal struggles against centralism and Serbian hegemonism. The KPJ's good fortune in these areas was an electoral protest against the regime. As an avowedly revolutionary party, the KPJ was the only outlet for the recusant nationalities in these areas. In the other areas of intense national disaffection, such as Croatia-Slavonia, Slovenia, and Bosnia-Hercegovina, the non-Serbs generally voted for the parties that best represented their national and confessional interests: the Croats for Radic's HPSS, the Slovenes for the Slovene People's Party, and the Bosnian-Hercegovinian Muslims for the Yugoslav Muslim Organization. Here the KPJ's showing was less impressive, Nevertheless, the KPJ still tended to discount the strategic potential of the national question and made no attempts to capitalize on this issue. The Communist leaders were overconfident of their ability to ride the continental red wave, and not inclined to reexamine their position.
Subsequent events repudiated the stance of the KPJ leadership. The postwar revolutionary wave in Europe had already reached its peak and was visibly receding. The defeat of the Red communes in Germany and Hungary and Soviet reversals in Poland hastened the stabilization of the anti-Communist governments and the social order that they safeguarded. But in Yugoslavia, where peasant insurgency was still seething – as in Croatia in 1920– the KPJ failed to appreciate the importance of national and peasant movements and lost the opportunity to impose itself on the rebel peasants. The Communist deputies in the Constituent Assembly, though seemingly confident, hardly appreciated the resilience of the regime that they continued to attack with an assortment of rhetorical devices. Nor did the KPJ leadership recognize the extent of the party's isolation, widened by the Communist inability to differentiate between the centralist government and the opposition parties. In the long run, the revolutionary bravado, as yet untested in direct conflict, proved counterproductive and exposed the party to government reprisals.
. . .
1. This section is greatly expanded in my work "The Communist Party of Yugoslavia during the Period of Legality (1919 – 1921)," in Ivo Banac, ed., The Effects of World War I: The Class War after the Great War; The Rise of Communist Parties in East Central Europe, 1919 – 1921 (Brooklyn, 1983), pp. 188 – 230. This work includes the most up-to-date bibliography of studies on the early history of Yugoslav Communism.