What was a significant factor in the
decision to go to war?

In the spring and summer of 2014, the Islamic State of Iraq and the Levant (ISIL) achieved a series of stunning military victories in northern Iraq. Particularly shocking to civilian observers was the news that comparatively small numbers of fighters prevailed against a significant Iraqi Army force. On paper, the larger Iraqi force had the clear advantage. In practice, their numerical superiority vanished as their forces fled, having no will to fight against the ISIL advance.

That was not the first time a conflict has been resolved by a strong—or weak—will to fight, nor will it be the last. Both the U.S. Army and the U.S. Marine Corps argue that will to fight is the single most important factor in war. Will to fight helps determine whether a military unit stays in the fight and also how well it fights. Once a conflict has begun, government leaders determine how and when wars end, and the political and economic variables—the national will to fight—determines whether the conflict continues.

The U.S. Army asked the RAND Arroyo Center to help U.S. leaders better understand and influence will to fight at both the national level and at the tactical and operational levels. The results of this exploration contain widely applicable lessons for the U.S. and its allies.
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