The seemingly unlikely emergence of a Czechoslovakia is largely the byproduct of diligent Czech nationalist activism, Allied postwar imperatives, and the sudden nature of Austro-Hungarian collapse. Of the Dual Monarchy's national minorities, the Czechs had an advantageous political position for the chaos of World War I. In the prewar period, the Czechs were able to develop a relatively detailed political program and assert some degree of national rights versus the German minority. The various prewar fights over the national question meant that the Czechs had a highly developed political discourse about national rights and a homeland. Czech national activists were able to posit that the Czech nation had a long historical pedigree (Bohemia) and paint other nationalities as either benign or pernicious to a future Czech state. The various writings of Masaryk such as Nová Evropa and those of other Czech intellectuals convinced the Allies that the Czechs had a clearer understanding of the nationalities issues than other groups. The activities of the Czech Legion and Masaryk's contributions to Allied intelligence also added a greater gloss to the Czechs than other groups. In particular, Masaryk and the Czech exile community were able to paint the Magyars as part of a conspirators with the Germans in repressing national minorities. This contributed to a perception among the Allies that the Slovaks would be better off in a union with the new Czech state. The Czech exiles argued they could integrate the Slovaks far better than either the Poles or the Hungarians. There was no real Slovak voice in these matters.

An enlarged Czech state was not an automatic given in the immediate postwar. Although the Allies favored an enlarged Czech state, the near total collapse of Austria-Hungary created a conditions that could undo all the plans of the Czech exiles. Fortunately for the Czech movement, the political leaders were able to swiftly take over the intact administrative and military apparatus of the dissolving Austro-Hungarian state. This was where the chronic ineptitude and weak state of the Hapsburgs played into the Czech hands; there was no supranational framework to resist this quiet Czech revolution after the abdication of the Hapsburgs. The Allies welcomed this development as Czech state was relatively stable and would be a lynchpin of the "little Entente" France was seeking to construct within Eastern Europe. The Slovak nationalists had no real choice in this matter and the Czech promised a degree of national unity and stability after a tumultuous war.

Sources

Hilde, P. S. "Slovak Nationalism and the Break-Up of Czechoslovakia". EUROPE ASIA STUDIES. 51, no. 4(1999): 647-666.

Zückert, Martin. "National Concepts of Freedom and Government Pacification Policies: The Case of Czechoslovakia in the Transitional Period After 1918". CONTEMPORARY EUROPEAN HISTORY. 17 (2008): 325-344.

I was looking for a question just like this only yesterday, here's a previous answer I found:

http://www.reddit.com/r/AskHistorians/comments/1y3w8y/why_did_the_czechs_and_slovaks_unite_into_one/

Thanks, I've often wondered about this. My grandparents called themselves Czechoslovakian, though they came over from Bohemia in the first decade of 1900, and have a family name that originates in Hungary.

So I've concluded that they were an 'ethnic minority', originally Hungarian, who made a new home in Bohemia, before emigrating to the US (over the course of a few or more generations). There's no one left to ask, all I know is that they didn't like to be called 'Slovaks'.