Momentous historical events have a great importance upon formation of national ideology regardless of political and social character of society. This is especially true for events, which, in a significant matter, contributed to formation of independent new states. The submitted paper is devoted to genesis of commemoration and celebration of happenings leading to foundation of Czechoslovakian Republic and to the their impact upon the official ideology of Czechoslovakian state. In this sense, three events are analysing: – Declaration of Foundation of Czechoslovak Republic, which was proclaimed on October 28 1918 and became the most important state holiday in Czechoslovakia; Martin Declaration, promulgated on October 30 1918 in city of Martin by representatives of Slovak community, who declared decision of Slovaks to join Czechs and create Czechoslovakia; lastly, so called Pittsburgh Agreement, concluded by representatives of Slovaks living in USA and later Czechoslovak president T. G. Masaryk on May 1918. Each of these historical events had its specific "life" and was viewed differently in dependence on political developments in Czechoslovakia. This was markedly noticeable in final year of pre-Munich Czechoslovakia, when external factors and domestic eccentric forces threatened a very existence of Republic. Pittsburgh Agreement, traditionally used as an argument in reasoning of Slovak autonomist to gain a greater independence from central government in Prague, became a pretense for asserting autonomy in October 1938. The paper is paying attention to impact of mentioned events upon political life in Czechoslovakia. Attention is also devoted to measures adopted by state organs to commemorate Declaration of Foundation of Czechoslovak Republic with aim to build-up and foster patriotic and cohesive sentiments among citizens of Czechoslovakia.