Conversation so far:
when was the expansion?
began to expand on the plains.
what expanded?
the Arapaho.
what was special about the expansion?
through trade, warfare, and alliances with other plains tribes.
who did they trade with?
the Arapaho made an alliance with the Cheyenne .
who did they go to war with?
the Kiowa (Niiciiheihiinenno'; Kiowa tribe: Niiciiheihiiteen) and invading Comanche.

Question: what types of things did they trade?
Self-contained rewrite: what types of things did Arapaho trade?