Complex sentence: During the next two centuries they were fully assimilated into the Hungarian population, their language disappeared, but they preserved their "Jassic" identity and their regional autonomy was preserved up until the year 1876.
Split into simpler sentences: During the next two centuries they were fully assimilated into the Hungarian population, their language disappeared, but they preserved their "Jassic" identity. Their regional autonomy was preserved up until the year 1876.