In “As I Ponder’d in Silence” in the “war” that Whitman says he will sing of in the second stanza. What does this mean?

The poet responds proudly that he does write about war, but a much grander and longer war than any other poet has ever attempted to address. This poet writes about the whole world, which is a battlefield encompassing struggles between life and death, body and soul. This is what sets him apart, and what will allow his words to endure.