Complex sentence: The Cheyennes went to Agent Fitzpatrick and asked for something to make up for this insult, he refused, but was later approached by the other tribes informing him that the Cheyenne were planning an attack.
Split into simpler sentences: The Cheyennes went to Agent Fitzpatrick and asked for something to make up for this insult. Fitzpatrick refused, but was later approached by the other tribes informing him that the Cheyenne were planning an attack.