Coronado's expedition through Texas was considered a failure because

Coronado's expedition greatly expanded Spain's knowledge of the North American continent, but because it found no gold and did not establish any new colonies, it was considered a complete failure at the time.

The way this small state - large state compromise guards against tyranny is that small states and large states have one note: i am sorry but i was not able to give you the full answer. but i got this answer from

The dethroned emperor!