On 23–24 November, the National Council declared "unification of the State of Slovenes, Croats and Serbs formed on the entire, contiguous South-Slavic area of the former Austria-Hungary with the Kingdom of Serbia and Montenegro into a unified State of Slovenes, Croats and Serbs". 28 members of the council were appointed to implement that decision based on National Council's adopted directions on implementation of the agreement of organization of the unified state with the government of the Kingdom of Serbia and representatives of political parties in Serbia and Montenegro. The instructions were largely ignored by the delegation members who negotiated with Regent Alexander instead.[5]

Stjepan Radić's Peasant Party participated in the National Council, but after it decided to merge with Serbia, they started to back off, calling the move foolish, and disputing the decision based on the fact that the Croatian Parliament never explicitly approved it.[7]

On 1 December, Regent Alexander proclaimed unification of "Serbia with lands of the independent State of Slovenes, Croats and Serbs into a unified Kingdom of Serbs, Croats, and Slovenes". As the National Council ceased to operate, it never formally ratified the proclamation, nor did the Parliament of Serbia, which took note of the declaration on 29 December 1918.[5]

The National Council's final important task was to appoint representatives to the Temporary National Representation in early 1919.[8]

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