I'm sure there is a thread about this somewhere and some very nice member will direct you to it.
But why are we here? I can't speak for others but I can give my (edit: very long-winded) answer. I'm here because the Killer Angels was a haunting and powerful book that despite being 11 I couldn't get out of my mind. I'm here because when I got a little bit older, I wanted to see whether or not the novel proclaiming that Stuart was "joy-riding" was really correct. I'm here because Shelby Foote and Bruce Catton can make history seem like a story. I'm here because making fun of Gods and Generals is a great balm for watching it.
I'm here because of the black men and women who fought and died for their freedom and who lived through a horrendous situation that I just can't imagine. I'm here for Harriet Tubman, Sojourner Truth, and all the other incredibly courageous people. I'm here because their legacy continues today.
I'm here because Sherman may be the single most quotable human being ever. I'm here because Frederick Douglas and Angelina Grimke were just so inspirational- and they remind me daily that whatever obstacles are placed in my path, people have overcome far worse to fly with the stars. I'm here because I can't imagine that young men charged across a field despite knowing that tomorrow they could be in the cold ground or lying in agony. I'm here because as Faraway Friend said on another thread, whenever I feel cold or hungry, I just think of those men. I'm here because sometimes I hope to walk the fields of Shiloh and listen hard to see if I can hear any long-dead bullets.
I'm here because I can't breathe when I hear about these mobs of starving women desperately rioting for bread- any bread- for they were starving and their families were dying. I'm here because Lincoln summarized the Union in a perfect two minute speech and I'm here because Grant's year long struggle with cancer makes him a hero in my book and I'm here because my heart wrenches when Lee paced desperately wanting to know whether or not he would stay in the Union and strike a hand against Virginia and I'm here because JEB Stuart makes me want to "jine" the cavalry.
I'm here because this was a period in our nation that was so great and terrible, beautiful, and devastating, when men and women took their destinies in their own hands and whether or not we like or agree with them- we have to respect that.
Oh, you guys may factor a little bit on why I'm here too.
Edit: No, no I don't have a life. And yes, yes I like making long-winded sermons as replies to simple questions. Why do you ask?