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.