“Mankind must put an end to war, or war will put an end to mankind.” –President John F. Kennedy

For most people war is an unthinkable horror. While generals must think realistically about war, an important duty for a political leader is to inspire others to do the unthinkable. Modifiers attempt to qualify war with words like limited, total, defensive, preemptive, just, unjust, good, bad, glorious, tragic, legal, illegal, etc. A U.S. Marine and Vietnam veteran who fought in a war that was described as “limited” estimated that during his 13-month tour he spent about 20 terrifying minutes under fire. On average he was wounded once every seven minutes. For half the young men in his platoon the war proved “total” because it ended their lives. The retired Marine officer told my military history seminar, “Anytime someone’s trying to kill you, it’s an intensely total war.”

At its essence, war is an act of force to compel the enemy to do your will. The words “force” and “will” are critically related. The goal (what you “will” the enemy to do) relates directly to the intensity of force required. Carl von Clausewitz, who authored this definition of war, experienced both the limited warfare of the 18th century Europe – a game of kings in which objectives were narrowly defined – and the Napoleonic wars conceived to overthrow monarchies and redraw the map of Europe.

The Cold War, which ended with a whimper rather than a bang, reflected the tradition of grand-national conflicts fought from 1789 to 1990: the French Revolutionary and Napoleonic wars, World Wars I and II, and the Cold War. These wars established and disestablished regimes and turned on ideological worldviews. Nations prevailed or fell, there were winners and losers, victors and vanquished. Scores of millions died; most of them civilians. The United States suffered a total of about one million deaths in wars during the same period, half by our own hands between 1861 and 1865. From the Union’s perspective, the totality of its objective required the destruction of rebel forces and the shattering of opposing political structures. Rhetoric embracing a “glorious cause” notwithstanding, the South pursued limited objectives. The Confederacy never intended to conquer the Union, nor did it desire to force slavery on northern states, or even to impose its political ideas on Washington. In the end the Union prevailed with its total war objectives pursued relentlessly by larger battalions.

Clausewitz also understood the naiveté and futility of trying to make war palatable. Wars inevitably intensify to the level of the strategic objective relative to the capabilities of respective participants. Humanity survived the Cold War because leaders of the major powers avoided a nuclear Armageddon, although the October 1962 Cuban missile crisis was a close call. Nevertheless, the Cold War claimed nearly 100,000 American lives, most lost fighting “limited wars” in Korea and Vietnam.

Today, ISIS’s ultimate goal is the destruction of America and the establishment of a global caliphate. If ISIS’s jihadists are not stopped, their path can easily be predicted. Initially they are targeting regimes in Damascus and Baghdad. From there it’s on to Amman and Cairo, Dubai, the wealthy Persian Gulf countries and Riyadh. Israel, seemingly abandoned by the United States, will be overrun despite its nuclear arsenal. Simultaneously, or shortly thereafter, the caliphate will use subversion and terrorism to consume European social democracies. Meanwhile, terrorist attacks against the United States, whether mandated by ISIS or inspired through its propaganda machine, will continue. It matters not a twit to ISIS leader Abu Bakr al Baghdadi that the Obama administration either cannot or will not recognize reality. As far as al Baghdadi and the ISIS fighters are concerned, the war is officially on.

A determined force consisting of fewer than two divisions spread from Aleppo to the outskirts of Baghdad can be defeated, but not without a concerted ground campaign. American air power can support such a campaign but air power will not bring decisive victory. Short of nuking most of Iraq and Syria, air power alone cannot destroy ISIS.

The first and most important thing about warfare is to understand the nature of the conflict and not misconstrue it for something more ideologically palatable or politically acceptable.

Semantics matter. Words define – and ultimately determine – the magnitude of wars. History is the final arbiter. How wars end and who prevails will be recorded in the victor’s words. The story those words tell will reflect the reality of the world inhabited by our children and grandchildren. That’s why it’s critical for the United States to get this war right and then to win it decisively.