The so-called Moro Crater Massacre took place during this campaign. Below is a short description lifted from Wikipedia.
The Moro Crater massacre is a name given to the final phase of the First Battle of Bud Dajo, a military engagement of the Philippine-American War, which took place March 10, 1906, on the isle of Jolo in the southern Philippines. Forces of the U.S. Army under the command of Major General Leonard Wood, a naval detachment comprising 540 soldiers, along with a detachment of native constabulary, armed with artillery and small firearms, attacked a village hidden in the crater of the dormant volcano Bud Dajo. More than 600 mostly unarmed Muslim Moro villagers (including many women and children) were killed by the Americans, of whom fifteen soldiers were killed and thirty-two were wounded.
Mark Twain, at the time, was vice-president of the Anti-Imperialist League. He wrote the following response to news of the incident.
(March 12, 1906) This incident burst upon the world last Friday in an official cablegram from the commander of our forces in the Philippines to our Government at Washington. The substance of it was as follows: A tribe of Moros, dark-skinned savages, had fortified themselves in the bowl of an extinct crater not many miles from Jolo; and as they were hostiles, and bitter against us because we have been trying for eight years to take their liberties away from them, their presence in that position was a menace. Our commander, Gen. Leonard Wood, ordered a reconnaissance. It was found that the Moros numbered six hundred, counting women and children; that their crater bowl was in the summit of a peak or mountain twenty-two hundred feet above sea level, and very difficult of access for Christian troops and artillery. Then General Wood ordered a surprise, and went along himself to see the order carried out. Our troops climbed the heights by devious and difficult trails, and even took some artillery with them. The kind of artillery is not specified, but in one place it was hoisted up a sharp acclivity by tackle a distance of some three hundred feet. Arrived at the rim of the crater, the battle began. Our soldiers numbered five hundred and forty. They were assisted by auxiliaries consisting of a detachment of native constabulary in our pay -- their numbers not given -- and by a naval detachment, whose numbers are not stated. But apparently the contending parties were about equal as to number -- six hundred men on our side, on the edge of the bowl; six hundred men, women and children in the bottom of the bowl. Depth of the bowl, 50 feet.Gen. Wood's order was, "Kill or capture the six hundred."The battle began-it is officially called by that name-our forces firing down into the crater with their artillery and their deadly small arms of precision; the savages furiously returning the fire, probably with brickbats-though this is merely a surmise of mine, as the weapons used by the savages are not nominated in the cablegram. Heretofore the Moros have used knives and clubs mainly; also ineffectual trade-muskets when they had any.
The official report stated that the battle was fought with prodigious energy on both sides during a day and a half, and that it ended with a complete victory for the American arms. The completeness of the victory is established by this fact: that of the six hundred Moros not one was left alive. The brilliancy of the victory is established by this other fact, to wit: that of our six hundred heroes only fifteen lost their lives.General Wood was present and looking on. His order had been. "Kill or capture those savages." Apparently our little army considered that the "or" left them authorized to kill or capture according to taste, and that their taste had remained what it has been for eight years, in our army out there - the taste of Christian butchers.The official report quite properly extolled and magnified the "heroism" and "gallantry" of our troops; lamented the loss of the fifteen who perished, and elaborated the wounds of thirty-two of our men who suffered injury, and even minutely and faithfully described the nature of the wounds, in the interest of future historians of the United States. It mentioned that a private had one of his elbows scraped by a missile, and the private's name was mentioned. Another private had the end of his nose scraped by a missile. His name was also mentioned - by cable, at one dollar and fifty cents a word.Next day's news confirmed the previous day's report and named our fifteen killed and thirty-two wounded again, and once more described the wounds and gilded them with the right adjectives.Let us now consider two or three details of our military history. In one of the great battles of the Civil War ten per cent. of the forces engaged on the two sides were killed and wounded. At Waterloo, where four hundred thousand men were present on the two sides, fifty thousand fell, killed and wounded, in five hours, leaving three hundred and fifty thousand sound and all right for further adventures. Eight years ago, when the pathetic comedy called the Cuban War was played, we summoned two hundred and fifty thousand men. We fought a number of showy battles, and when the war was over we had lost two hundred and sixty-eight men out of our two hundred and fifty thousand, in killed and wounded in the field, and just fourteen times as many by the gallantry of the army doctors in the hospitals and camps. We did not exterminate the Spaniards -- far from it. In each engagement we left an average of two per cent. of the enemy killed or crippled on the field.Contrast these things with the great statistics which have arrived from that Moro crater! There, with six hundred engaged on each side, we lost fifteen men killed outright, and we had thirty-two wounded-counting that nose and that elbow. The enemy numbered six hundred -- including women and children -- and we abolished them utterly, leaving not even a baby alive to cry for its dead mother. This is incomparably the greatest victory that was ever achieved by the Christian soldiers of the United States.Now then, how has it been received? The splendid news appeared with splendid display-heads in every newspaper in this city of four million and thirteen thousand inhabitants, on Friday morning. But there was not a single reference to it in the editorial columns of any one of those newspapers. The news appeared again in all the evening papers of Friday, and again those papers were editorially silent upon our vast achievement. Next day's additional statistics and particulars appeared in all the morning papers, and still without a line of editorial rejoicing or a mention of the matter in any way. These additions appeared in the evening papers of that same day (Saturday) and again without a word of comment. In the columns devoted to correspondence, in the morning and evening papers of Friday and Saturday, nobody said a word about the "battle." Ordinarily those columns are teeming with the passions of the citizen; he lets no incident go by, whether it be large or small, without pouring out his praise or blame, his joy or his indignation about the matter in the correspondence column. But, as I have said, during those two days he was as silent as the editors themselves. So far as I can find out, there was only one person among our eighty millions who allowed himself the privilege of a public remark on this great occasion -- that was the President of the United States. All day Friday he was as studiously silent as the rest. But on Saturday he recognized that his duty required him to say something, and he took his pen and performed that duty. If I know President Roosevelt -- and I am sure I do -- this utterance cost him more pain and shame than any other that ever issued from his pen or his mouth. I am far from blaming him. If I had been in his place my official duty would have compelled me to say what he said. It was a convention, an old tradition, and he had to be loyal to it. There was no help for it. This is what he said:Washington, March 10. Wood, Manila:- I congratulate you and the officers and men of your command upon the brilliant feat of arms wherein you and they so well upheld the honor of the American flag. (Signed) Theodore Roosevelt.His whole utterance is merely a convention. Not a word of what he said came out of his heart. He knew perfectly well that to pen six hundred helpless and weaponless savages in a hole like rats in a trap and massacre them in detail during a stretch of a day and a half, from a safe position on the heights above, was no brilliant feat of arms - and would not have been a brilliant feat of arms even if Christian America, represented by its salaried soldiers, had shot them down with Bibles and the Golden Rule instead of bullets. He knew perfectly well that our uniformed assassins had not upheld the honor of the American flag, but had done as they have been doing continuously for eight years in the Philippines - that is to say, they had dishonored it.The next day, Sunday, -- which was yesterday -- the cable brought us additional news - still more splendid news -- still more honor for the flag. The first display-head shouts this information at us in the stentorian capitals: "WOMEN SLAIN MORO SLAUGHTER.""Slaughter" is a good word. Certainly there is not a better one in the Unabridged Dictionary for this occasionThe next display line says:"With Children They Mixed in Mob in Crater, and All Died Together."They were mere naked savages, and yet there is a sort of pathos about it when that word children falls under your eye, for it always brings before us our perfectest symbol of innocence and helplessness; and by help of its deathless eloquence color, creed and nationality vanish away and we see only that they are children -- merely children. And if they are frightened and crying and in trouble, our pity goes out to them by natural impulse. We see a picture. We see the small forms. We see the terrified faces. We see the tears. We see the small hands clinging in supplication to the mother; but we do not see those children that we are speaking about. We see in their places the little creatures whom we know and love.The next heading blazes with American and Christian glory like to the sun in the zenith:"Death List is Now 900."I was never so enthusiastically proud of the flag till now!
Martha note #2: FYI, Lexington-based writer James R. Arnold, author of Jungle of Snakes: A Century of Counterinsurgency Warfare from the Philippines to Iraq, will publish a book on the Moro Campaigns next year.