For the first time since its establishment as a nation, and following four successive victories against various Arab conventional armies between 1948 and 1973, Israel was forced to withdraw militarily from south Lebanon in May 2000. This thesis investigates the defeat of the Israeli Defense Force by a guerilla army, Hezbollah. Rarely are the causes of defeat on the modern battlefield simply a case of military failure. Specifically this study will focus on the combination of factors that in unison forced the withdrawal of the Israeli Defense Force from Lebanon. The study concludes that a combination of political, military and social factors combined to force Israel to withdraw from Lebanon. A failure by Israel's politicians to correctly identify the true nature of the problem and to link political goals to achievable military objectives condemned the 1982 invasion from the outset. Additionally, the Israeli Defense Force was slow to adapt to guerilla warfare throughout the 18-year war, preferring to rely on the proven methods of prior conventional wars to achieve victory. Moreover, the social impact of a long and unwinnable war without a just cause impacted severely on Israeli society weakening support for an Army whose historical role had changed from protector to aggressor.