Complex sentence: At the time of this treaty, the boundaries between Spanish America and the United States had not yet been established, so this treaty formally includes the Creek chiefs to attend the negotiation for running the Florida-Georgia boundary line with Spain.
Split into simpler sentences: At the time of this treaty, the boundaries between Spanish America and the United States had not yet been established. This treaty formally allowed the Creek chiefs to acknowledge the negotiation for running the Florida-Georgia boundary line with Spain.