[8] Ante Trumbić served as president of the committee,[9] but its most prominent member was Frano Supilo, the co-founder of the ruling Croat-Serb Coalition (HSK) in Croatia-Slavonia.

Supilo advocated a federation consisting of Serbia (including Vojvodina), Croatia (encompassing Croatia-Slavonia and Dalmatia), Bosnia and Herzegovina, Slovenia, and Montenegro.

At the same time, the committee learned that the Triple Entente promised the Kingdom of Italy territory (parts of the Slovene Lands, Istria, and Dalmatia) under the Treaty of London to forge an alliance with that nation.

That year, Russia sued for peace following the Russian Revolution, while the United States, whose President Woodrow Wilson advocated the principle of self-determination, entered the war.

[13] The signatories included Korošec, and two other prominent Slovenian political leaders – the Governor of the Duchy of Carniola, Ivan Šusteršič, and Janez Evangelist Krek.

[5] The SSP leader, Ante Pavelić, praised the declaration in the Croatian Sabor a week after its debut in Vienna as an expression of a democratic spirit awakened in Europe by enlightened Russia.

Mahnič deemed the establishment of a common South Slavic polity of some sort inevitable and was predominantly concerned with issues of "ethnic and confessional cohabitation" in such a state.

Besides moving the issue of South Slavic unification beyond its Croatian framework and demonstrating that the Slovenian political actors were not necessarily loyal to the empire, the declaration impacted the thinking of authorities in Serbia and of the Yugoslav Committee.

[14] The Triple Entente was looking for ways to achieve a separate peace with Austria-Hungary and thereby detach it from Germany, presenting the Serbian government – exiled on the Greek island of Corfu – with a problem.

It was faced with the substantial risk of a trialist solution of the South Slavic lands within Austria-Hungary in the case of such a separate peace treaty, thereby cancelling any chance of fulfilment of the proclaimed Serbian war objectives.

They held a series of meetings on Corfu from 15 June to 20 July, attempting to reach consensus despite radically different views on the system of government in the proposed common state.

No agreement on the issue was reached, so the resulting Corfu Declaration glossed over the matter, leaving it to the Constituent Assembly to decide by an unspecified qualified majority.

[21] As the central authority of Austria-Hungary gradually disintegrated in 1918, provincial national councils were established (including one for Slovenia by the Yugoslav Club) to fill the power vacuum, introducing a parallel administration by July.