Bohemia was the most industrialized part of Austria and Slovakia was the most industrialized part of Hungary – however at very different levels of development. Furthermore, the Hungarians were far more determined to assimilate the Slovaks than the Austrians were to assimilate the Czechs. Around the start of the 20th century, the idea of a "Czecho-Slovak" entity began to be advocated by some Czech and Slovak leaders after contacts between Czech and Slovak intellectuals intensified in the 1890s. Despite cultural differences, the Slovaks shared similar aspirations with the Czechs for independence from the Habsburg state. In 1917, during World War I, Tomáš Masaryk created the Czechoslovak National Council together with Edvard Beneš and Milan Štefánik (a Slovak astronomer and war hero). Masaryk in the United States (and in United Kingdom and Russia too), Štefánik in France, and Beneš in France and Britain worked tirelessly to secure Allied recognition. About 1.4 million Czech soldiers fought in World War I, 150,000 of which died. More than 90,000 Czech and Slovak volunteers formed the Czechoslovak Legions in Russia, France and Italy, where they fought against the Central Powers and later with White Russian forces against Bolshevik troops. At times they controlled much of the Trans-Siberian railway, and they were indirectly involved in the shooting of the Russian tsar and his family in 1918. Their goal was to win the support of the Allies for the independence of Czechoslovakia. They succeeded on all counts. When secret talks between the Allies and Austrian emperor Charles I (r. 1916–18) collapsed, the Allies recognized, in the summer of 1918, the Czechoslovak National Council would be the kernel of the future Czechoslovak government. The independence of Czechoslovakia was officially proclaimed in Prague on 28 October 1918 in Smetana Hall of the Municipal House, a physical setting strongly associated with nationalist feeling. The Slovaks officially joined the state two days later in the town of Martin. A temporary constitution was adopted, and Tomáš Masaryk was declared president on 14 November. The Treaty of St. Germain, signed in September 1919, formally recognized the new republic. Ruthenia was later added to the Czech lands and Slovakia by the Treaty of Trianon in June 1920. There were also various border conflicts between Poland and Czechoslovakia due to the anexion of Zaolzie region. The new state was characterized by problems with its ethnic diversity, the separate histories of the Czech and Slovak peoples and their greatly differing religious, cultural, and social traditions.