I was doing living history in the barracks at Fort Larned, visiting with the folks trickling through the Fort on a quiet Saturday afternoon when I got a simple question with a complicated answer. After I had shown a couple around the room and given them my time-tested barracks interpretive notes about the soldiers, their lifestyle, and their equipment during the Indian Wars, a woman asked at an above-normal volume and with a degree of outrage, "Why did they kill the women and children?"
I was somewhat surprised by the question, and smiled because I knew it would be a challenge to answer. I told her "It's complicated," and proceeded to give the longest extemporaneous answer I'd ever given. The answer is multi-faceted and complex. It's impossible to pin down any one specific answer because it's really a chili pot full of influences that lead to the type of violence seen in the Indian Wars.
Here is an attempt to explain why women and children were killed in the Indian Wars.
The Strategic Level
I can think of three reasons why women and children became targets in the Indian Wars on a broad, strategic level.
1. The Need to Attack - The overarching goal of the Indian Wars was, for better or for worse, to end Indian peoples' control of the Plains and other areas of the west. In so doing, the military can only really do two things: deter attack through their mere presence (the threat of violence), or to actually attack. In some situations, the army was able to defuse potential violence through its presence, as was done by the Army escorting wagon trains at Fort Larned in 1864. However, so long as Indian peoples resisted through guerilla warfare and raiding, the call for military retribution grew more and more intense from American citizens and politicians, in some cases culminating in military action. When the regular army wouldn't intervene, state-led volunteer units were raised; these were virtually undisciplined mobs that were indiscriminate in their actions. Units raised in Kansas and Colorado come to mind.
2. Total War - Especially after the Civil War, with officers like General Sherman, then the head of the Army, well versed in the strategy of Total War, were accustomed to a style of warfare that allowed infrastructure, not just military personnel, to become targets. The purpose, of course, was to make continued resistance so horrible and unbearable that they would give up. The terror stemmed from both the deaths incurred during an attack, but more so from the deprivation of food and shelter. In order to survive, destitute people had to come in to the Indian Agencies to survive.
3. Winter Campaigns - The byproduct of total war was the winter campaign championed by General Philip Sheridan. The winter campaign's purpose was to deprive Indians of supplies, shelter, and food exactly when they depended on it the most, villages became primary targets. As such, women and children were present and thus subject at least to collateral damage and at most, to murder.
Realities on the battlefield made women and children targets, too. Because Plains Indians engaged in light cavalry tactics on the battlefield, because they knew the land better than the whites, and because they could still claim victory at the end of the day even if they left their opponents holding the battlefield (because taking and holding ground was not their primary objective), they were exceedingly difficult targets for the Army to engage. The warriors seemed to appear and disappear at will. Even in situations where the Army was permitted to engage the Indians, it was exceedingly difficult to find them. This difficulty was a major reason why Custer attacked when he did at Washita in 1868 and at Little Bighorn in 1876; his opponent was so difficult to find, so he had to attack while he knew where they were. Custer had been unsuccessful in finding anybody to engage in Kansas in 1867 after the situation at Fort Larned unraveled into war.
The other tactical reality was the limited amount of intelligence available to military organizers. By the time one got close enough to inspect a village, he risked being spotted, in which case, the village probably would not be there by the time the troops arrived. Attacking headlong into unclear situations became necessary for the Army, and there were consequences: getting in over one's head, killing innocent people, or even attacking the wrong tribe altogether.
Most of the Army officers were veterans of the Civil War, and not only were they accustomed to Total War, many were ambitious and sought success in their careers. And what could be better than getting your name in the papers for a smashing, righteous victory? Not only did this recognition help them in their careers, many of the officers had political ambitions. Generals Grant, McClellan, and Hancock all ran for President. There is reason to believe Custer was thinking about running at the time of the Little Bighorn campaign.
It's also true that some people are just evil, pure and simple. They would take any opportunity to kill another person and mutilate the body just for their own amusement. This happened at Sand Creek, and I'm sure it played a part in other battles as well. Nobody told the volunteers at Sand Creek to cut off a woman's breast and wear it as a hat, or a man's scrotum and use it as a tobacco pouch; the people who did these things clearly had issues that took them far beyond their duties as soldiers. Frustration, bias, and revenge must also have played a role, for there were nearly constant murders, abductions, and attacks that stemmed from the Indian side as well as the white. Retribution for one attack tended to escalate violence as revenge killings created a feedback loop that amplified over time. There is also a place for ignorance, simply not knowing exactly who they were fighting against because of the pressure to do something and the unavailability of useful reconnaissance.
So while there are many factors at play, the short answer is that the Army, when ordered to attack, had to attack when they had the opportunity, and women and children happened to be present many times when those opportunities arose. That, coupled with indifference or malice on the part of the army personnel, whether organized or on an individual scale, made women and children targets.
There is also the possibility that soldiers either did not or could not make a distinction between men and women in the heat of combat.
At this point, the visitor asked, "But wouldn't attacking helpless people like children and the elderly just make them want to fight more?"
Yes it would! However, the reasons why, and why that didn't really matter in the long run, are again complicated, and they're the other part of the equation.
Tribal Organization and Polarization
As is the case in nomadic hunter-gatherer groups throughout history, the societies are roughly egalitarian. Although chiefs are respected by many, their power is limited to those who choose to follow them. This is possible in a hunter-gatherer society because everyone has roughly equal access to resources if he or she is willing to go and get them. Agrarian societies, where stockpiling food creates an imbalance in wealth, tend toward a pyramid-shaped society with identifiable classes; thus, feudalism, monarchy, despotism, and so on. So when a Plains Indian decided he or she didn't like the way one chief was handling business, they could choose to follow another. While this might be a natural progression of a society over time to grow and divide, this polarization within Plains Indian societies in this historical moment proved consequential.
While some people preferred a peaceful solution and were willing to go into the Indian Agencies and receive the annuities offered to them by the Government in exchange for treaty agreements designed mainly to get them out of the way of the advancing white society, others rejected that kind of subservience, and chose independence. Within the Cheyenne, specifically, chiefs like Black Kettle advocated a peaceful solution early; realizing that lasting independence was not possible, he was eager to get the best deal for his people to live peacefully. The Cheyenne were well known for their friendliness in the early days. However, the warrior faction of the tribe, the Dog Soldiers, was more inclined toward independence. Following the unprovoked massacre at Sand Creek, the Dog Soldiers gained more clout in the years that followed.
The tension pulling the Cheyenne apart in the 1860s was not unique. It had happened to virtually every tribe faced with the same dire situation. As one example, precisely the same thing had happened with the Sauk and Fox tribes when they were moved onto their reservation in Iowa; Keokuk wanted to maintain peace and Black Hawk wanted to wage war. The result of war was that both groups were punished together. The same happened to the Cheyenne.
The Warrior Tradition and its Consequences
Plains Indian culture placed value in warrior skills. Thus, there was a culturally-ingrained tradition of a warrior seeking honor and distinction. A young man was compelled to show his courage, bravery, and skill through counting coup in a variety of ways: stealing horses, touching an enemy in battle, etc. Raiding wagons on the Santa Fe Trail and stealing goods was one manifestation of this impetus. While the tradition might come across as playful youth looking for a good time, or "boys will be boys," its darker aspects should not be overlooked.
Certain actions, whether part of an overarching strategy of harassment or else actions perpetrated by factions or individuals, were more serious. These acts of bravery, however, were frowned upon by those affected by them, and they are largely responsible for the outcry for military proteciton by white society. Particularly, white people were routinely murdered, raped, abducted, mutilated, and forced into slavery by Indians. Understandably, this created a culture of fear and anger against the Indians that manifested itself in both organized and individual "revenge" of one sort or another.
The U.S. government, meanwhile, was conflicted in its policies towards Indians. On the one hand, people were shouting for military protection and action against "hostile" Indians. On the other hand, peace was much less expensive for the government, even at the cost of providing annuities for thousands of people every year. Fort Larned, as an Indian Agency site and as a site for distribution of annuities in the Medicine Lodge Treaty was part of this solution. The government see-sawed between the two policies, emphasizing one, then the other through the Indian Wars. Grant in particular was influenced by those who pursued the peace agenda through the Office of Indian Affairs, but eventually he turned to the military to end lingering conflicts.
This two-pronged strategy allowed the U.S. Government to emphasize either the carrot or the stick, as necessary. "Come in and be peaceful and get gifts, or, if you choose violence, we will punish you." When the Dog Soldiers continued violence in 1868, it culminated in the attack at Washita in November, 1868. In that battle, it was not the Dog Soldiers whom Custer attacked, but the peaceful village of Black Kettle's followers. Washita happened because of all of the above reasons on strategic, tactical, and personal levels, and I think it's fair to say that many battles throughout the Indian Wars that were begun in a premeditated fashion by the Army were similar in their multi-faceted reasoning.
While it is arguable that the military tended to increase violence with any action they took other than simply deterring attack, the true cause for the end of fighting was the utter destitution of the tribes opposing the U.S. Government. Deprived of food with the near-exctinction of the bison, elements of tribes that fought for independence ultimately could not sustain their war effort. The same had recently been true for the Confederates a decade prior. While the unavailability of food probably took the tribes 99% of the way to the brink, the military, through continued pressure, helped push them over the edge. In that sense, tribal resistance to U.S. dominion throughout the Indian Wars was really just a last, desperate, and ineffective gasp of the tribes to protect their autonomy, doomed to fail from the outset.
Even in the face of smashing victories like Little Bighorn, overall victory was impossible. The nomadic way of life dictated that the tribe had to move to support themselves and, just as importantly, their horses. The thousands of people gathered at the combined village at Little Bighorn were compelled to break up in order to have pastures for their horses, and thus, gave up their greatest strength: the sheer size of their village. The Army, capable of producing food elsewhere and ship it to where it was needed, did not have such problems, allowing it to move forces as needed, when needed. Additionally, there was the calculus of populations and attrition: army forces were replaceable and effectively numberless in the long term, warriors were not replaceable in the short term.
But if they had not resisted at all, would Plains Indians have been better off? Would it have spared the lives of some women and children? A historian isn't allowed to answer a question like this, so I leave it up to you to answer that for yourself.