Ethnos
What must you do when your hand is at the 10-card limit?
The recruiting section's hand-limit rule settles this directly.
- Ethnos rulebook · Rulebook · Recruiting Allies
You must play a Band of Allies, because recruiting is not allowed at 10 cards. Any band of 1 to 10 cards is legal, even a single card, and it does not need to place a Control marker.