It's a piece by Gustav Holst from his suite The Planets. I admit I prefer works from the Classical & Baroque periods with an occassional fondness for the Romantic but there are a few 20th Century pieces that I enjoy. The Planet suite is one of them. The opening piece starts off in 5/4 time but shifts to 5/2 & then later 3/4 (told ya I liked uncommon time signatures). Its dissonance & dark haunting melodies have made it one of Holst's most recognizable works & in it you can almost hear premonitions of William's Imperial March from the Star Wars soundtracks. Wikipedia's media section on The Planets' page has the first four movements of the suite (Mars, Venus, Jupiter & Uranus respectively) in "play in browser" as well as downloadable formats. If you scroll down to the 2002-2003 season you'll find The Peabody Institute has MP3's of The Planets suite as well. But for your convenience here's the Toronto Symphony Orchestra's vid of their performance of Mars, the Bringer of War (Part 1 & Conclusion) (& on the right side of the screen you'll see vids of them doing more of The Planets suite if you care to listen - & I do recommend checking out Jupiter if nothing else).
What follows will be about war. One in which we are currently engaged.