Complex sentence: The level of resistance and road conditions slowed the army's advance to an average of 20 kilometers a day, one of the lowest speeds of Soviet forces during the invasion; it advanced a depth of 200 kilometers into Manchuria.
Split into simpler sentences: The level of resistance and road conditions slowed the army's advance to an average of 20 kilometers a day, one of the lowest speeds of Soviet forces during the invasion. During the invasion, it advanced a depth of 200 kilometers into Manchuria.