When your civilization builds an embassy in a rival's capital city, or when a rival builds one in your capital, you can negotiate Diplomatic Agreements with that civilization. There are four kinds: Military Alliance You agree to declare war on a despised third party. Right of Passage You agree to allow his or her military units to move through your territory and use your transportation network (roads and railroads). Trade Embargo An agreement that neither of you will trade with or allow trade with a third party. Mutual Protection Pact An agreement to declare war upon any civilization that attacks your partner. There is a fifth item that you can trade through your Embassies: Communications. These are introductions to a third civilization you can grant or receive from a rival.