Complex sentence: Although they could not hold the city, the 24th Infantry Division achieved a tactical victory by delaying the North Koreans, which bought time for other American divisions to establish a defensive perimeter around Pusan further south.
Split into simpler sentences: Although they could not hold the city, the 24th Infantry Division achieved a tactical victory with the successfully delay the North Koreans. This bought time for other American divisions to establish a defensive perimeter around Pusan further south.