From UFStarfleet LCARS
The Jankata Accord was an accord that essentially stated that "no species shall enter another Quadrant for the purpose of territorial expansion." This accord was signed by both the Federation and the Cardassians.
The Dominion War however, negated all agreements between the Federation and the Cardassian Union. This permitted Starfleet Command and the Federation Council to sanction the formation of United Federation Starfleet in the Delta Quadrant withut breaching the accord.