The Coalition Compact was a treaty of alliance signed in 2155 by United Earth, the Confederacy of Vulcan, the Andorian Empire, and Tellar. The Coalition Compact established the Coalition of Planets, a mutual-defense pact created in the wake of a Romulan incursion into local space.
The details of the Compact state that the Coalition was forbidden from engaging in a pre-emptive strike against other nation. It would be this clause that stopped the Coalition from attacking the Romulan Star Empire after the surprise strike against Coridan Prime as there was little evidence that attributed the Romulans to the attack. (ENT novel: The Good That Men Do)