He had been told, in terms specific enough to be credible, that flying this flag would protect his camp.

The flag was not merely symbolic.

It was a specific diplomatic instrument — a visible signal within a framework of meaning that both parties to the communication were supposed to understand.

He raised the flag because he understood the framework.

He believed that the framework was real — that flying an American flag over a Cheyenne camp would communicate to American soldiers what it was supposed to communicate: that this camp was friendly, that these people had placed themselves under American protection, that attacking them would violate a specific commitment made by American officials.

The soldiers attacked anyway.