sentences:  According to historian Timothy Snyder, the annexation of Vilnius by Poles pushed Lithuanian politicians from political towards ethnic understanding of the nation and gave arguments to radical politicians in Lithuania and also in Poland.Lithuania refused to recognize Central Lithuania.Polish-Lithuanian relations began to normalize after League of Nations negotiations in 1927, but it was not until the 1938 ultimatum issued by Poland that Lithuania was forced to establish diplomatic relations with Poland and thus "de facto" accept its neighbor's borders.