If you've seen the movie, you need to read the book now to flesh out the ill-advised, ill-conceived and ill-fated military arrest raid into Mogadishu. If you haven't seen the movie either, watch it, then read this book. Mark Bowden did tons of research in order to piece together the events as they happened on that day. The Rangers and Special Forces (Delta Force) operators involved in that arrest raid and subsequent SHTF firefight experienced combat at a level of intensity and ferocity probably unseen by American foot soldiers since the Tet Offensive or, more likely, the Korean War. Bowden's investigative reporting, collected into one cohesive narrative, brings to mind Cornelius Ryan's work on famous operations of WWII. The overlapping point-of-view of multiple participants in modern battle is similar to Hell and Gone (though this is non-fiction). Why our armed forces were in Somalia is just as valid a question as why our troops are in Iraq now. But this is not a book about policies and politics...it's about men in combat.
You also should read The Longest Day: The Classic Epic of D-Day (non-fiction).