It Europe itself,the rise of national awareness at the end of eighteenth century Spread across Europe from west to east.
By the middle of the century , nationalist leaders and thinkers were already thinking in terms of an exclusivist doctrine calling for the "nation" to correspond with the "state,
That is, to make political borders correspond with ethnic or linguistic borders.
Carrying out such exclusivist ethnic nationalism was approached in a number of ways in various settings, and a number of small states moved toward policies of ethnic exclusion in the nineteenth century. It was on the peripheries of the great European empires ( including especially the Ottoman Empire) that a sharp-edged,ethnicity-oriented policy led to a variety of policies of forced assimilation, expropriation of property, violence, and in several cases, mass killing.
Following the destruction or mutiilation of such established Eouropean empires as Austria-Hungary, Ottoman Turkey , Russia , and Germany in wake of World War I , and the simultaneous creation of nearly a dozen allegedly national, but in fact mostly multinational small states, the policy of ethnic cleansing was introduced into modern Europe as a regular policy and in a certain sense "legitimized." The newly created, reestablished, or radically enlarged "successor states" particularly Czecho- Slovakia, Yugoslavia, and Romania in the center; Bulgaria, Greece' and Turkey in the south; and to a lesser degree Poland and Lithuania in the north expelled hundreds of thousands of minority inhabitants from their newly acquired or