The article refers to the reactions of the Hungarian community in Transylvania during 1918-1920, with the entry of this historical region into the composition of the Kingdom of Romania. The First World War generated a real political rupture and a fundamental demographic-social change in Europe, the disappearance of the Austro-Hungarian Empire being considered a truly exceptional event. In this complicated context, the Hungarians in Transylvania tried to crystallize various political projects, meant to best represent their long-term interests. The content of the article makes a series of demographic clarifications and insists on the moment of the Assembly in Cluj, from December 22, 1918, when the representatives of the Hungarians from Transylvania tried to offer a reply to the Great National Assembly of the Romanians in Alba Iulia, on December 1, 1918. Through the political event in Cluj, the Hungarians in Transylvania made perhaps one last attempt to keep the region of Transylvania under their political control. But it was far too late, as long as Romania had gained a considerable strategic-political advantage over a Hungary under the impact of a severe internal crisis.