The First World War (1914-1918) did not diminish the chauvinism of the Hungarian government, but it did bring the faith of Slovak politicians in the possibility of reforming and democratizing Hungary to an end. It speeded up the change in the orientation of Slovak policy. Before the war, this occurred on the soil of the Hungarian state. But it supported such concepts by which the Slovaks could achieve an autonomous position in a federal Austria-Hungary.

In foreign affairs the majority of Slovak politicians expected positive initiatives from Russia. From the beginning of the twentieth century cooperation with Czech political parties, organizations and individuals also increased significantly. The years before World War I saw the maturation of a new generation of politicians who would lead the political life of Slovakia after 1918, namely Milan Hodža, who belonged among the co-workers of the pretender to the Habsburg throne, Franz Ferdinand, Andrej Hlinka, Vavro Šrobár, Ivan Dérer and others.

Map of Austria-Hungary Empire in 1914:
Map of Austria-Hungary Empire in 1914

The first public speeches advocating the formation of a common state for the Slovaks and Czechs were made abroad, in France, England and in the USA. Since the end of the 19th century up to the First World War more than half a million Slovaks emigrated to the United States. In the democratic conditions there, they matured and from the distance they realized how unbearable the situation in Hungary was and what was the actual position of the Slovaks there.

In 1915 the representatives of the Slovak and Czech ethnic organizations signed the Cleveland Agreement concerning the establishment of a common federal state. The Pittsburgh Agreement, signed in May 1918 by Slovak and Czech emigrants and Tomáš Garrigue Masaryk, proclaimed the autonomous position of Slovakia within a democratic Czecho-Slovak Republic.

The idea of a common state for the Czechs and Slovaks, linguistically closely related nations, had a rational basis. It could diminish the German hold upon the Czech lands and open the way for it to the east and south-east. For the Slovaks it would end forced magyarization and a non-democratic regime so that the development of their culture and national emancipation would become easier and come about more quickly.

The representatives of both nations collaborated very closely in the resistance abroad against the Habsburg Monarchy. The Slovak, Milan Rastislav Štefánik – an astronomer and a general in the French Army, was T. G. Masaryk’s closest collaborator and the first to initiate a Czecho-Slovak resistance. Many Slovaks fought in the Czecho-Slovak legions in France, Italy and Russia.

By the end of the war, the idea of dissolving the Habsburg Monarchy and the establishment of an independent Czecho-Slovakia was fully supported by the allied powers, the United States, England, France and Italy. In this spirit labored also the domestic resistance. On 28 October 1918 the Czecho-Slovak National Committee in Prague proclaimed the existence of Czecho-Slovakia.

On 30 October not yet having received information concerning events in Prague, the Slovak National Council also declared in Martin, its desire to join Slovakia with the Czech lands in one common state. The Czecho-Slovak Republic was one of the many successor states of the Austro-Hungarian Empire. Its development brought to an end the hundreds of years affiliation with the Kingdom of Hungary.