How does Whitman's poetry engage with the Civil War, specifically "Song of Myself" and "Crossing Brooklyn Ferry"?

Walt Whitman engages with the Civil War in a number of places, most specifically in his "Drum Taps" poems. However, the Civil War loomed large in much of his poetry, both before and after it occurred. His epic "Song of Myself" is, in some ways, his understanding of the potential for war and an attempt to get the people of the world, more specifically, the people of the north and south in the United States, to relate to one another before the country could be torn apart. Because of this, the specter of the Civil War haunts much of his work, including "Song of Myself," despite the fact that the earlier drafts of the poem were published well before the war broke out. In an effort to help people relate to and respect one another, Whitman establishes a clear motif of connection from the very start of the poem. However, Section 18 focuses specifically on his attempts to connect himself to both the North and South, acting as a conduit to connect them to each other. In this section, he states he is "[o]ne of the Nation of many nations, the smallest the same and the/ largest the same" as well as "[a] Southerner soon as a Northerner." Even more specifically, he calls himself "Yankee," "Kentuckian," "Louisianian or Georgian" but also "Hoosier, Badger,/ Buckeye." Whitman repeatedly moves back and forth across the great divide between the north and south, and even opens his identity to further north and west, claiming his "Kanadian snow-shoes" and himself "Comrade of Californians" as he is "ever regardful of others." Through this movement, he attempts to smooth the divide and create a path between any and all people.
Even in the 1855 edition of the poem, Whitman's Section 18 attempts to unify as he claims "I play not marches for accepted victors only, I play marches for/conquer'd and slain persons [...] beat[ing] and pound[ing] for the dead," as well as the living. Here he shows that the winners and losers, living and dead, are one in the same for him and should be for each other.
While Whitman's "Crossing Brooklyn Ferry" focuses more specifically on the life of New York City, his idea of transcendental connection between all living things continues, particularly in Sections 3 and 4. In Section 3, he describes experiences of crossing "the river of old," detailing the sights and sounds of nature, human or otherwise and, again, showing his kinship with all of it. In Section 4 he writes:

These and all else were to me the same as they are to you, I loved well those cities, loved well the stately and rapid river, The men and women I saw were all near to me, Others the same—others who look back on me because I look’d forward to them

Once again, Whitman establishes his camaraderie with the world. The river is any river. The person is any person. The cities are any cities. He loves any and all the same. Whitman spent his entire life trying to unify the world through his words. Even after the Civil War had come and gone, he continued to write and revise in an effort to help others see each other as he sees all of them: as both capable and worthy of kindness, respect, and love.