THERE is little need for another study of what happened at the Battle of the Little Big Horn, considered from the stand-point of objective results, for they have already been repeatedly cataloged. And, except for the action on Custer Field, the how of the event has been largely cleared up. What remains in violent controversy is the why of the results. This leads us directly to the mental reactions of the participants in the face of what they encountered from the time they left the Yellowstone until the battle was over.If we wish to understand why Custer, Reno, Benteen, or any of the troop commanders did what they did, we must, in imagination, ride at their elbows and try to see what they saw at any given time and place, the nature of the terrain, what they knew or believed, about the position and numbers of the enemy, the whereabouts of the different detachments of the regiment, and try to understand their doubts and perplexities resulting from insufficient information. In addition to this we must constantly have in our own minds a panoramic view of the whole area involved, as well as a fairly accurate idea of the minor details of the topography that are of military significance, and remember that the responsible officers learned of these details, for the most part, only as they came to them.The present study is, therefore, concerned chiefly with this why. It represents an effort to do what, as far as we are aware, has never been attempted before except for certain limited phases of our subject. That is to say, I have sought to explain in a systematic way the why of the battle not so much by dint of quotation from the sources as by subjecting these sources to a rigid analysis in order to discover what they seem to spell after all definite inconsistencies have been canceled out. It is a large order that leaves ample room for self-deception and other types of error.