Complex sentence: As a last resort, the South Koreans established another defence line at Gangbuk-gu, but were defeated at the Battle of Miari and, after three days of resistance, the North Koreans drove into Seoul.
Split into simpler sentences: As a last resort, the South Koreans established another defence line at Gangbuk-gu, but were defeated at the Battle of Miari. After three days of resistance, the North Koreans drove into Seoul.