Jesús Balsinde's
Alba de América at
spanish.apolyton.net/ is an example of a scenario where two tribes are allied at the start of the game and forbidden to negotiate and therefore cancel the alliance.
In events you use the 'double negotiation' event:
@IF
NEGOTIATION
talker=French
talkertype=HumanOrComputer
listener=English
listenertype=HumanOrComputer
@THEN
@ENDIF
@IF
NEGOTIATION
talker=English
talkertype=HumanOrComputer
listener=French
listenertype=HumanOrComputer
@THEN
@ENDIF
…and Cheat > Edit King > Edit Treaties > Alliance, and Cheat > Edit King > Set Attitude to make the initial diplomacy fall into place.
This of course puts your tech trading partly out of reach. You could use a 'received tech' and 'give tech' event to force a trade...
@IF
RECEIVEDTECHNOLOGY
technology=0
receiver=French
@THEN
JUSTONCE
GIVETECHNOLOGY
receiver=English
technology=1
@ENDIF
@IF
RECEIVEDTECHNOLOGY
technology=1
receiver=English
@THEN
TEXT
The French receive Chemical Warfare from the English. The English receive Advanced Interrogation from the French.
ENDTEXT
JUSTONCE
GIVETECHNOLOGY
receiver=French
technology=0
@ENDIF
This is untested however, but should work in theory.