In the previous spring, 1845, Colonel Kearny left Fort Leavenworth with several companies of dragoons, and marching with extraordinary celerity reached Fort Laramie, whence he passed along the foot of the mountains to Bent’s Fort and then, turning eastward again, returned to the point from whence he set out.  While at Fort Larantie, he sent a part of his command as far westward as Sweetwater, while he himself remained at the fort, and dispatched messages to the surrounding Indians to meet him there in council.  Then for the first time the tribes of that vicinity saw the white warriors, and, as might have been expected, they were lost in astonishment at their regular order, their gay attire, the completeness of their martial equipment, and the great size and power of their horses.  Among the rest, the Arapahoes came in considerable numbers to the fort.  They had lately committed numerous acts of outrage, and Colonel Kearny threatened that if they killed any more white men he would turn loose his dragoons upon them, and annihilate their whole nation.  In the evening, to add effect to his speech, he ordered a howitzer to be fired and a rocket to be thrown up.  Many of the Arapahoes fell prostrate on the ground, while others ran screaming with amazement and terror.  On the following day they withdrew to their mountains, confounded with awe at the appearance of the dragoons, at their big gun which went off twice at one shot, and the fiery messenger which they had sent up to the Great Spirit.  For many months they remained quiet, and did no further mischief.  At length, just before we came into the country, one of them, by an act of the basest treachery, killed two white men, Boot and May, who were trapping among the mountains.  For this act it was impossible to discover a motive.  It seemed to spring from one of those inexplicable impulses which often actuate Indians and appear no better than the mere outbreaks of native ferocity.  No sooner was the murder committed than the whole tribe were in extreme consternation.  They expected every day that the avenging dragoons would arrive, little thinking that a desert of nine hundred miles in extent lay between the latter and their mountain fastnesses.  A large deputation of them came to Fort Laramie, bringing a valuable present of horses, in compensation for the lives of the murdered men.  These Bordeaux refused to accept.  They then asked him if he would be satisfied with their delivering up the murderer himself; but he declined this offer also.  The Arapahoes went back more terrified than ever.  Weeks passed away, and still no dragoons appeared.  A result followed which all those best acquainted with Indians had predicted.  They conceived that fear had prevented Bordeaux from accepting their gifts, and that they had nothing to apprehend from the vengeance of the whites.  From terror they rose to the height of insolence and presumption.  They called the white men cowards and old women; and a friendly Dakota came to Fort Laramie and reported that they were determined to kill the first of the white dogs whom they could lay hands on.