In MP we have also two lines of thoughts, on which we had very on-the-line-of-flaming debates: one on the "thou shalt respect all the treaties you make or your honour will be corrupted forever" and one on the "I'll say we're best friends and then backstab you and steal your girlfriend". So you'll often see separate MP games that say clearly (if the creator makes the things right) if in the specific match the rules allow or not violating Naps and treaties (also called Vegas/Machiavellian diplomacy). The first ones make more strightforward games, the second ones might make the game more chilly, interesting and thematic as you don't know who are really your friends (possibly... none if they see the opportunity
) so... you decide what you prefer!