This monograph determined that the tactical and strategic experience of the Israeli Defense Force (IDF) since 1981 was relevant to the future operational environment of the U.S. Army. The IDF's experiences are relevant because the Israeli Army was similarly equipped and organized to the heavy units in the U.S. Army, both then and now. Israel faced a similar full spectrum threat, and the IDF had to adapt to enemies who switched to asymmetric methods in order to overcome Israel's conventional military superiority. The IDF of 1981 paralleled the U.S. Army of the 2000 in many ways. It was a mechanized heavy force designed to conduct operations against a Soviet armed and equipped enemy. It fought and defeated some of those enemies decisively eight years previously. Beginning with the invasion of Lebanon (Operation "Peace for Galilee"), the IDF discovered that there were no peer competitors willing to fight it on its own terms. The nature of war changed for the IDF in sometimes unexpected ways, and it struggled to adapt to its changing operational environment. The IDF operational environment became much more complicated, because while it retained the old threats in the form of its Arab neighbors, it added sustained guerrilla war and civil insurrection.