Peace and Violence Among the 19th Century Saints

https://www.lds.org/topics/peace-and-violence-among-19th-century-latter-day-saints?lang=eng&query=scholar

This link is a church article which talks about many issues with regards to the church and violence in the early days of the church.   It shows the story from both sides, talking about the Mormons from the side of victims of violence, but also talks about times when early Saints perpetrated violence.  It talks about many things which you would think the church wouldn't talk about.  This includes discussion of the Danites and their roll in violence.  It also gives a very good summary of the Mountain Meadows Massacre. 
Violence against members of the Church in the early days resulted in much loss of life and persecution.  It also resulted in loss of property, which was never reimbursed.  Violence resulted in the Mormons becoming refugees on several occasions.  This included the expulsion from Nauvoo, and the resultant hardships in Iowa and Nebraska.  It is estimated that during this time, one in twelve Mormons passed away because of this hardship.  That the U.S. would allow such violence against a religious group is unheard of in the history of our country, but it did happen.  Mormons achieved a relative period of peace by fleeing to the Rocky Mountains.
In 1857, there was again misunderstanding between the Mormons and the U.S. which lead to the march of U.S. troops against the Mormons to put down rebellion.  It was in this atmosphere that the Mountain Meadows Massacre.  The violence against others is not acceptable, and was not authorized by the church.

Haun's Mill Massacre

Haun's Mill was a tragedy.  It is called a massacre, because it took place in a time of truce.  "Because the attack was unprovoked in a time of truce, had no specific authorization, and was made by a vastly superior force with unusual brutality, it has come to be known as 'The Haun's Mill Massacre.'  (Blair, Alma R., Encyclopedia of Mormonism)  Haun's Mill was a small isolated Mormon community.  That the attack was possible was a result of the people not heading the prophet's instruction of the isolated communities gathering to Far West.  This request was not passed on to the Saints at Haun's Mill as presented in this discourse of Henry B. Eyring. 

http://www.lds.org/media-library/video/doctrine-and-covenants/section-120-church-history?lang=eng

Blair explains the events of the day:
Thirty to forty LDS families were at Haun's Mill when some 200 to 250 militia from Livingston, Daviess, and Carroll counties, acting under Colonel Thomas Jennings, (also sheriff of Livingston county) marched against the village. Assuming that an earlier truce still held, the residents were surprised by the late afternoon attack. Church leader David Evans' call for "quarter" was ignored, and the villagers were forced to flee for safety. The Mormon women and children fled south across a stream into the woods, while the men gathered in the blackSmith shop, but found it a poor place for defense because the Missourians were able to fire through the widely spaced logs directly into the group huddled inside.
Seventeen Latter-day Saints and one friendly non-Mormon were killed. Another thirteen were wounded, including one woman and a seven-year-old boy. (ibid.)
This is event was even more heinous because of some of the murders, including that of children:  "After the initial attack, several of those who had been wounded or had surrendered were shot dead. Members of the militia entered the shop and found ten-year-old Sardius Smith, eight-year old Alma Smith, and nine-year-old Charles Merrick hiding under the blacksmith's bellows. Alma and Charles were shot (Charles later died), and William Reynolds put his musket against Sardius's skull and blew off the top of his head, killing him.  Reynolds later explained, "Nits will make lice, and if he had lived he would have become a Mormon."  Seventy-eight year old Thomas McBride surrendered his musket to militiaman Jacob Rogers, who then shot McBride and hacked his body apart with a corn knife. Several other bodies were mutilated or clothing stolen, while many women were assaulted. Houses were robbed, wagons, tents and clothing were stolen, and horses and livestock were driven off, leaving the surviving women and children destitute.  (Wikipedia)