The chapter on the American Civil War describes what may have been Lincoln’s finest moment as president. During the summer of 1864, Northern public support for the war was collapsing. If Lincoln did not make a peace deal with the Confederacy, including renouncing the 1863 Emancipation Proclamation which freed the Confederate slaves, he was guaranteed to lose the November presidential election to the anti-war Democrat George McClellan.But Lincoln refused to negotiate, specifically refusing to budge on the Emancipation Proclamation. The Proclamation had enhanced the Union’s military power by encouraging blacks to fight for the Union and against the Confederacy. Lincoln feared that if he backtracked on the Proclamation, it would inspire the Southern states to break any peace agreement and demand full independence. Such an outcome would, in Lincoln’s mind, lead to the unraveling of the entire Union. Lincoln preferred losing the fall election and sacrificing his political fortune on the altar of freedom to winning a Pyrrhic electoral victory and see his beloved Union become, in the words of his predecessor James Buchanan, “a rope of sand” disintegrating as each state went its own way. Fortunately, General William Sherman’s great victory at Atlanta in September 1864 boosted Union public support for the war, and saved Lincoln’s presidency as well as perhaps the Union itself.Another fascinating case is Winston’s Churchill’s decision to fight on against Germany in late May 1940. Things looked quite bleak for Britain. France was falling, and Germany was racking up a string of other conquests of Belgium, the Netherlands, Denmark, and Norway. The Soviet Union was at this point a German ally. America was not yet even close to entering the war. Germany appeared poised to invade Britain after conquering France, and Britain’s prospects for fending off such an attack were dim. Some of Britain’s highest leaders, such as Lord Halifax, urged Churchill to negotiate with Hitler in order to save the country from conquest. But Churchill refused. He thought that Hitler would not abide by any war-ending peace deal. Hitler would demand that Britain hand over its navy and its colonial possessions; after doing so Britain would be at Germany’s mercy. So, because he deeply distrusted Germany, and despite Britain’s precarious position, Churchill decided to take his chances and continue to fight, rather than strike a deal with Hitler. It was during the months that followed that Churchill gave his most stirring speeches encouraging Britons to fight on: “We shall not flag or fail. We shall go on to the end. We shall fight in France, we shall fight on the seas and oceans, we shall fight with growing strength in the air, we shall defend our island, whatever the cost may be, we shall fight on the beaches, we shall fight on the landing grounds, we shall fight in the fields and in the streets, we shall fight in the hills; we shall never surrender.” More tersely, he also declared, “If this long island story of ours is to end at last, let it end only when each one of us lies choking in his own blood upon the ground.”Singing Norman Whitfield and Barrett Strong’s famous song “War,” Edwin Starr declared, “War! What is it good for? Absolutely nothing.” Some people argue that war happens because it reflects fundamental aggressiveness in human nature. Some argue that war happens because two countries or societies simply hate each other. And some argue that technology causes war, that once weapons are invented countries seek reasons to use them.This book provides a different answer to this question, explaining the political function served by war. I argue that countries fight wars to solve problems of mistrust. This is a longstanding observation, that mutual fear causes countries to launch wars. This book expands on past work, arguing that fear also shapes the way that countries fight and end their wars. When belligerents fear that the other side will not abide by a war-ending peace settlement, this fear pushes them to reject negotiations and instead pursue the absolute defeat of their adversary. Eliminating the adversary solves the mistrust problem.That being said, though adversaries sometimes try to solve their mistrust problems by fighting wars to the finish, the book also provides caveats as to why this is not always an attractive foreign policy. Certainly, sometimes it is the best and only thing to do—the absolute defeat of Germany, Italy, and Japan in World War II being perhaps the best examples. However, sometimes you can inflict total defeat on a rogue leader’s military, but then face a costly insurgency after the conventional war has ended. Think Iraq and Afghanistan. Sometimes you can use other means to deal with mistrust which are much cheaper than fighting a war, and are sufficiently effective. We mistrusted the Soviet Union, but deterrence kept them from attacking America or its allies for decades. And a state which appears to be untrustworthy and dangerous may actually pose much less of a threat than we had thought, thus the costs of a war to oust the leader would not be worth bearing. Iraq’s lack of weapons of mass destruction or connections to terrorist groups stands out as a clear example of this kind of paper tiger.