Myths and Stereotypes vs Historical Reality.
“Is it true that in 1917-1918 the Ukrainian borders were formed by the Soviet Ukraine, that is, the Bolsheviks?”

The territory of the Ukrainian state in the twentieth century was originally shaped as a result of the Central Council’s (Central Rada) activity (March 1917 - April 1918) that created the Ukrainian People's Republic (UPR). The Rada and the Bolsheviks, who seized power in the city of Petrograd, did not hurry to recognize each other: the Bolsheviks defined the Rada as "bourgeois," although claiming to express the national rights of Ukrainians; the Rada considered the Bolsheviks as usurpers, because power in the new Russia should have belonged to the entire socialist democracy, not a single party. However, when trying to capture Ukraine and establish its authority, the Soviet Ukrainian government referred namely to the borders of the UPR. They covered the provinces with a predominantly Ukrainian population, which was based on the official pre-revolutionary statistics.

After the overthrow of the tsar the Central Rada, organized in March 1917, became the core of the Ukrainian national movement. It had to identify certain objective criteria for determining the borders of Ukraine. Taking into account the undeniable fact that in the nineteenth - early twentieth centuries in Europe occurred formation of the nation states, as well as absence of somehow outlined territory of Ukraine in the Russian Empire (see the article: "After the 1917 revolution, did the Bolsheviks really give Ukraine its current South-East?" http://likbez.org.ua/after-the-1917-revolution-the-bolsheviks-gave-ukraine-its-current-south-east.html), it should be admitted that the only possible objective criterion for determining Ukraine's borders was the national composition of population. Under conditions of the ongoing world war careful (at a level of the parish or at least county) following this criterion was impossible. Therefore, the Central Council has solved this issue in general terms, and the basic administrative unit for the territorial allocation of Ukraine became the province.

During the first general census of the Russian Empire (1897) one of the indicators was the native language (“Malorussian” / “Little Russian” or “Velikorussian” / Great Russian), which became an objective criterion for determining the national composition. It turned out that Ukrainians were the majority of population in nine provinces. Moreover, in Poltava, Kiev, Ekaterinoslav, Kharkiv, Podolsk, Kherson, Volyn, Chernihiv provinces Ukrainians constituted the absolute majority of the population (from 53.5% to 93.0%), and in Tauris province – the relative (42.2%). According to the declaration of the Central Council of 11 May 1917, namely within the boundaries of these provinces had to be established "Ukraine," and it was emphasized that "withdrawal of the non-Ukrainian parts from the provinces and, conversely, adding to the Ukrainian region the Ukrainian parts of the adjacent provinces - Kholm, Grodno, Minsk, Kursk, Voronezh, the Kuban region and so on is to be carried out by the Regional Council [Rada], in agreement with the Provisional Government and population of these areas." In November, this principle was enshrined in the Third Universal of the Central Rada.

Thus the ethnographic criterion has become a major factor in determining the borders of Ukraine, but he was limited by the administrative division that existed since the times of the Russian Empire. Immediately after the seizure of power the Bolsheviks actually agreed with this criterion, too. Hoping to seize power in Ukraine in the second half of November, Stalin insisted that namely the Kiev Regional Committee of the RSDLP (b) (Russian Social Democratic Labour Party) should be the initiator of the All-Ukrainian Congress of Soviets, and the participants should be "the citizens of Kiev, Odessa, Kharkiv, Ekaterinoslav and others," that is, it was about all 9 provinces.

An attempt to seize power at the All-Ukrainian Congress of Soviets that was convened in Kiev in the beginning of December, 1917 failed. Then the Bolsheviks took another path:  the pro-Bolshevik deputies of the All-Ukrainian Congress went to Kharkiv and joined the regional congress of Soviets of the Donetsk-Kryvyi Rig basin that was held in this city. New Congress was proclaimed All-Ukrainian, there was elected the Central Executive Committee of the Ukrainian (Soviet) People's Republic. On December 17 (Old Style), 1917 it formed a government - People's Secretariat, which aimed to unite "for the struggle against the Central Council the workers in all areas claimed by the Central Council."

Source: http://likbez.org.ua/in-1917-1918-border-of-ukraine-formed-the-soviet-ukraine-ie-the-bolsheviks.html