Peace Treaty

A basic treaty when not in war.

Min Relation: varies with covenant aggression and many other factors

Advantage: Not at war :)

Non-aggression Pact

A simple promise of no war between two covenants.

Min Relation: 57.5

Advantage: A friend that is less likely to go to war with you

Mutual Protection Pact

A covenant automatically declares war on any covenant that declares war on one of their protected covenants.

Min Relation: 70.0

Advantage: A good friend that will automatically go to war with anyone that goes to war with you or raids you

Disadvantage: If another covenant declares war on your friend, you will automatically declare war on them.  So you can get dragged into wars.

Alliance

A covenant automatically declares war on any covenant that goes to war with one of their protected covenants.

Min Relation: 80.0

Advantage: A very good friend that will automatically go to war with anyone that gets into a war with you regardless of who the aggressor is.  You can also win the game with allies without needing to destroy them.

Disadvantage: Any war that your ally gets into, you will also.

Note: alliances take precedence over mutual protection pacts.