In terms of chords and melody, This Is War is more complex than the typical song, having above average scores in Melodic Complexity, Chord-Melody Tension, Chord Progression Novelty and Chord-Bass Melody.
This Is War is written in the key of F♯ Major. According to the Theorytab database, it is the 9th most popular key among Major keys and the 16th most popular among all keys. Major keys, along with minor keys, are a common choice for popular songs. The three most important chords, built off the 1st, 4th and 5th scale degrees are all major chords (F♯ Major, B Major, and C♯ Major). See the F♯ Major Cheat Sheet for popular chords, chord progressions, downloadable midi files and more!