During General Sherman’s March to the Sea during the American Civil War, Sherman wrought as much destruction as he could. His goal was to sap the South of both the means and the will to fight. He scoured the countryside for supplies and killed livestock. Rail twisted around trees became known as a “Sherman necktie.” His motto was simple: “War is hell.” Although McNamara would not disagree with Sherman, his fifth lesson is that proportionality should be a guideline in war.

If two things are proportional, they are equivalent or roughly equal. McNamara suggests that damage inflicted in a time of war should be proportional to one’s goals. He does not advocate “taking it easy” on one’s opponents. He is not suggesting a nation fail to get the job done. He is saying we should strive to kill only as much as necessary to achieve our objectives.

In 1945, the United States began bombing Japan using incendiary weapons. 51% of Tokyo was destroyed, killing 100,000. 58% of Yokohama was incinerated. Virtually all of Toyama was wiped out. 40% of Nagoya was burnt to a crisp. 67 Japanese cities suffered massive losses during the United States’ firebombing campaign. After all of that, the US dropped two atomic bombs, leveling Hiroshima and Nagasaki.

World War II’s Pacific Theater might have been the most brutal conflict in human history. Truman and American military leaders had no clue how close Japan was to collapse and the Japanese had offered no evidence of giving up. All of this was done to end the war before American soldiers had to hit the beaches of the Japanese Home Islands. The US saved the lives of 100,000 theoretical American soldiers by killing one million Japanese civilians.

Thankfully, there aren’t many examples in recent history that relate to this lesson, although we would be wise to heed it for many of our current foreign policy disputes. Every time North Korea is in the news or Iran’s alleged nuclear program is discussed, someone invariably suggests that we launch a preemptive strike, possibly with nuclear weapons. Do we want to anger other nations, increase our risks of blowback, betray our nation’s ideals, and kill tens of thousands of innocent civilians to achieve our goals? We do not possess a goal worth those costs.

Proportionality is a critical concept to fighting a just war, if such a thing exists. Losing the moral high ground in today’s interconnected world is an invitation for conflict, terrorism, and ruin. And it would be well-deserved. Victory takes care of a lot of things, but it won’t turn war criminals into heroes.

Jump to a lesson:
Introduction
Lesson 1: Empathize with Your Enemy
Lesson 2: Rationality Will Not Save Us
Lesson 3: There’s Something Beyond One’s Self
Lesson 4: Maximize Efficiency
Lesson 5: Proportionality Should Be a Guideline in War
Lesson 6: Get the Data
Lesson 7: Belief and Seeing Are Often Both Wrong
Lesson 8: Be Prepared to Re-examine Your Reasoning
Lesson 9: In Order To Do Good, You May Have To Engage in Evil
Lesson 10: Never Say Never
Lesson 11: You Can’t Change Human Nature
Conclusion