FORT BENNING, Ga. — “A GREAT deal of intelligence can be invested in ignorance when the need for illusion is deep,” the novelist Saul Bellow once wrote. We should keep that in mind when we consider the lessons from the wars in Iraq and Afghanistan — lessons of supreme importance as we plan the military of the future.

Our record of learning from previous experience is poor; one reason is that we apply history simplistically, or ignore it altogether, as a result of wishful thinking that makes the future appear easier and fundamentally different from the past.

We engaged in such thinking in the years before the attacks of Sept. 11, 2001; many accepted the conceit that lightning victories could be achieved by small numbers of technologically sophisticated American forces capable of launching precision strikes against enemy targets from safe distances.

These defense theories, associated with the belief that new technology had ushered in a whole new era of war, were then applied to the wars in Afghanistan and Iraq; in both, they clouded our understanding of the conflicts and delayed the development of effective strategies....