Fighting briefly lulled after the 1996 conflict as Hezbollah recovered from the fighting, but the movement's logistics were "resilient," and the group dramatically escalated the level of violence thereafter. While Hezbollah performed 100 attacks from 1985–1989 and 1,030 attacks in the six-year period from 1990 to 1995, it launched 4,928 attacks from 1996–2000, including at least 50 attacks per month for three years and over 1500 attacks in 1999 alone. After abandoning the tactic of frontal assaults on SLA and IDF outposts around 1987, Hezbollah resumed the practice a decade later with radically changed tactics. On 18 September 1997, Hezbollah attacked 25 outposts simultaneously and used ATGM teams to target reinforcements. By the end of the occupation, Hezbollah was using heavy weapons and engaging in hours-long firefights with the enemy. In October 1998, Hezbollah first deployed an explosively formed penetrator, a sophisticated and powerful IED that can penetrate almost any armor. Hezbollah considers 1998, 1999, and 2000 to be their most successful years of insurgency, and in 1997 and 1998 combined Israeli and SLA casualties exceeded those of Hezbollah. A research paper by analyst Iver Gabrielson argues that by the late 1990s, Hezbollah had become "tactically proficient" organization. By identifying and targeting Israel's weak point, casualties, Hezbollah was able to win a war of attrition. Amid escalating violence, poor morale, and intense political pressure at home, the war in Lebanon became too much for Israel. On 6:48 am of May 24, 2000, the IDF departed southern Lebanon for the first time in 18 years, and the SLA militia immediately collapsed. Although Hassan Nasrallah had once promised to "slaughter" SLA members in their beds, there were no revenge killings.