Treaties define your relationship with the other factions. By default, no treaties are in place and the factions are neutral towards each other.
Integrity[]
Integrity measures the current value of your word-of-honor as a faction leader. If you keep your promises and do not betray your friends, your integrity will remain high. Attacking factions you have pledged Blood Truce or signed Treaties with will rapidly lower your integrity rating, and other faction leaders will no longer be eager to make such agreements with you.
Note that there is no dishonor in attacking a sworn enemy with whom you have not pledged Blood Truce; only breaking an agreement can lower your Integrity.
Treaties[]
Treaty of Friendship[]
A Treaty of Friendship is intended to secure a permanent and lasting friendship between two factions. Once you have signed a Treaty, you will receive commerce benefits with your new friends. You may not, without diplomatic repercussions, enter the territory of a faction you have a Treaty with.
A Treaty of Friendship terminates only if one faction attacks another or refuses a valid demand for withdrawal.
Pact of Brotherhood[]
A Pact of Brotherhood (or Pact of Sisterhood) is the closest form of diplomatic relationship you can form with another faction. Pact Brothers may enter each other's territory freely, may stack with each other's units, and may enter each other's bases (and receive repairs there).
Pact Brothers are expected to defend one another from enemy attack. They receive double commerce between their bases, and are often willing to share technological research.
A Pact can be terminated at any time (the right-click menu on the Commlink menu is one way to do it), but at the moment of termination all of your units will automatically be shipped home from your former Pact Brother's territory, and vice Versa.
Vendetta[]
Vendetta is a state of war between two factions. If you have pronounced Vendetta on a faction (or another faction has pronounced it against you), expect to be Attacked.
Blood Truce[]
Blood Truce marks an end to Vendetta between two factions. It a promise not to attack one another for a limited period of time. After about 15-20 years, a Blood Truce will expire and the two factions will continue as Neutrals unless they again attack one another.
Technically, Blood Truce does not restrict you from entering another faction's territory, but other faction leaders may not see things that way.