Originally posted by Hygro
Diplomatic agreements must require the proper ingame mechanisms. Mutual Protection Pacts must not happen until nationalism, and must be signed in game. Military Alliances require writing, and must be signed in game. Both need embassies to do so ingame.
Similiar agreements such as a full on embargoes(no techs, gold, whatevers) would require you sign an embargo and then have the other part made official for all the other nations you have embassies with to see. Ocean right of passages would require that you have writing and an embassy, but you would not need to sign the actualy ROP because that encompasses land and using the other's road system.
Border agreements probably wouldn't be limited, but to make it official you'd need writing and an embassy.
Hell, maybe no diplomatic agreement is binding unless signed ingame. Something along these lines.