Latgalian language
Originally Latgalians were a tribe living in modern Vidzeme and Latgale. It is thought that they spoke the Latvian language, which later spread through the rest of modern Latvia, absorbing features of the Old Curonian, Semigallian, Selonian and Livonian languages. The Latgale area became politically separated during the Polish–Swedish wars, remaining part of the Polish–Lithuanian Commonwealth as the Inflanty Voivodeship, while the rest of Latvians lived in lands dominated by Baltic German nobility. Both centuries of separate development and the influence of different prestige languages likely contributed to the development of modern Latgalian as distinct from the language spoken in Vidzeme and other parts of Latvia.
Latvia
In the post-war period, Latvia was made to adopt Soviet farming methods. Rural areas were forced into collectivisation. An extensive programme to impose bilingualism was initiated in Latvia, limiting the use of Latvian language in official uses in favour of using Russian as the main language. All of the minority schools (Jewish, Polish, Belarusian, Estonian, Lithuanian) were closed down leaving only two media of instructions in the schools: Latvian and Russian. An influx of labourers, administrators, military personnel and their dependants from Russia and other Soviet republics started. By 1959 about 400,000 people arrived from other Soviet republics and the ethnic Latvian population had fallen to 62%.