Original sentence: On 13 October, Syria launched the 13 October attack, a major operation involving its army, air force (for the first time since Zahle's siege in 1981) against Aoun's stronghold around the presidential palace, taking advantage of the internal Christian war between Aoun and the LF, where hundreds of Aoun supporters were killed by Syrian troops
Edited sentence: On 13 October, Syria launched the 13 October attack, a major operation involving its army, air force (for the first time since Zahle's siege in 1981) against Aoun's stronghold around the presidential palace, taking advantage of the internal Christian war between Aoun and the LF, where hundreds of Aoun supporters were executed by Syrian troops who showed no mercy attacking the Christians of Lebanon