Complex sentence: This violation angered the tribes who felt that the promises that were made to them by the United States Government were not being upheld, and this led to a retaliation through the murder of the Indian agent for that area, thereby inciting the Yakima War.
Split into simpler sentences: This violation angered the tribes who felt that the promises that had been made to them by the United States government were not being honored. This led to a retaliation through the murder of the Indian agent for that area, thereby inciting the Yakima War.