The end of the American civil war: nobody left to die

This is the kind of history that grabs my analytic attention. Emphases mine … (unfortunately, DeLong forgot to credit the author)

Brad DeLong's Semi-Daily Journal: Study War...

... If you want to know about the American Civil War, you need to hear something like this:

Not even the deep South was strongly for secession. Those voting for delegates to Georgia's secession convention, for example, were almost evenly split--and you can bet that the African-Americans who did not get to vote for delegates were overwhelmingly against secession. Because there was no Southern consensus for secession, Lincoln was able to hold the border--Missouri, Kentucky, Maryland, western Virginia, eastern Tennessee--by making it a war for the Union. And the war began with a Confederacy of 5 million whites (and 4 million African-Americans) and a Union of 21 million whites (and 1 million African-Americans).

The Union mobilized 2.6 million soldiers--24% of its total male population. The Confederacy mobilized 900 thousand soldiers--36% of its white male population. Armies would march down secured railroad lines or navigable waterways until they ran into other armies. Because they could not function far from railhead or water-based supply depots, strategic outflanking moves were rare. When armies clashed, casualties were horrendous, but decisive victories impossible. The rifled musket was too good in defense, and the large size of the armies made them too clumsy in pursuit.

The result was that the armies fought, and soldiers died in battle, afterwards of wounds, and in camp of disease. By April 1865 300,000 Union soldiers were dead, 300,000 more were disabled by wounds, about 200,000 had deserted and returned home, and 400,000 had been discharged--leaving 1.4 million with the colors. By April 1865 300,000 Confederates were dead, 300,000 more were disabled by wounds, and 300,000 had deserted or returned home--leaving next to nobody with the colors to surrender to Grant and Sherman. The war was then over.

In a world where defensive is strong, a war ends when one army is gone. What happens in a world where offense is strong and defense is weak (Nuclear weapons, bioweapons, even IEDs)? How does a war end then? How will the Iraqi Civil War end?