The poem treats a war as if it were a person who has simply fallen ill and died. The speaker says "the war I mourn," which is a surprising thing to hear. Wars are usually something people want to see end, but here the speaker seems to grieve its passing, perhaps because it gave life a shape or a purpose, or because of what it meant to those who lived through it. The poem doesn't say, so we're left to wonder.
The ending is quietly sharp. Instead of a grand peace treaty, the war goes out through "spotted fever," an ordinary, almost shabby death. And at the burial, people "sat late disputing." Even now, they can't agree, perhaps about who was right or what the war was really about. The mood is dry, sad and a little ironic. It suggests that arguments outlive the conflicts that caused them, and that mourning and quarrelling can happen at the same graveside.