We present a statistical study of planetary alignments and the outbreak of war, with emphasis on those involving pairs of an inner and outer planet. The study is based on data from the Correlates of War project (Sarkees & Wayman, 2010), representing approximately 1,000 engagements between 1816–2007. Through a series of analytical approaches, multiple nominally statistically significant results are found, including a recurring signature for Mars. Notably, conflicts are found to begin under Mars-Pluto Squares and Mars-Uranus Sextiles at approximately 1.5 times the expected frequency (p = .006 – .008, N = 524, h = .10 – .11). While the results are suggestive, this study does not decisively indicate astrological correlations to the outbreak of war. We believe this to be the most comprehensive statistical study of the astrological correlates of a collective historical phenomenon yet undertaken. We consider in detail the limitations of this study, including the testing of multiple variables, and suggest that a study such as this is important both from a critical perspective of astrology and in terms of astrological understanding.