War is Hell!
If one wanted to we could look further in history, you will see why Indians were not trusted.
Julesburg Massacre.
Fort Mimms.
Massacre of the Fort Dearborne school children.
Massacre of the Pennsylvania school children during the Conspiracy of Pontiac.
Fort Sandusky massacre.
Fort St Joseph Massacre.
Fort Ouiatenon Massacre.
Fort Michilimackinac Massacre.
Fort Venango Massacre.
Fort Le Boeuf. No massacre as they escaped to Fort Pitt.
Fort Presque Isle Massacre. (Treachery of the worst sort)
http://en.wikipedia.org/wiki/Pontiac%27s_War#Small_forts_taken
http://en.wikipedia.org/wiki/Indian_massacre
Here is a list of other massacres. Be careful as they often do not tell the whole story. For example, at the Council House massacre in San Antonio, it makes it sound like the Indians were lured in then killed.
What happened was the Indians brought in some captive white children WITH THEIR FACES BURNED OFF. This is what set off the massacre.