Complex sentence: A differentiation of separate East Slavic groups begins to take place in the later medieval period, and an East Slavic dialect continuum developed in the Polish-Lithuanian Commonwealth, with the Ruthenian language emerging as a written standard.
Split into simpler sentences: A differentiation of separate East Slavic groups begins to take place in the Polish-Lithuanian Commonwealth. At this stage, there was an East Slavic dialect continuum, with the Ruthenian language emerging as a written standard.