Alternative theories of the location of Great Moravia propose that the core territory of "Great Moravia", a 9th-century Slavic polity, was not (or was only partly) located in the region of the northern Morava River (in present-day Czech Republic). Moravia emerged after the fall of the Avar Khaganate in the early 9th century. It flourished during the reign of Svatopluk I in the second half of the century, but collapsed in the first decade of the 10th century. "Great Moravia" was regarded as an archetype of Czechoslovakia, the common state of the Czechs and Slovaks, in the 20th century, and its legacy is mentioned in the preamble to the Constitution of Slovakia.