Complex sentence: During the night part of red troops began to breakthrough to the east, in Sviyazhsk direction, another part-to the north, to the Arsk, but most of the red troops were captured by Whites.
Split into simpler sentences: During the night part of red troops began to breakthrough to the east, in Sviyazhsk direction, with another group escaping to the north, to the Arsk. However, most of the red troops were captured by Whites.