To Trade or Not to Trade?

[RLucid]

Often it's clearly in your interests to trade. Even with "enemy", say Carthage offers ceasefire, after Julii take Caralis. Then offering trade rights, allows extortion of a small tribute. Trading with Carthage, helps them fight Scipii, and improves Julii financial position, helping rapid development and faster expansion. It also gives a financial incentive against Carthage, re-capturing the town, and re-opening hostilities, which might help keep the sideshow quiet, until you're ready to storm their Capitol.

However, if you conquer Gaul as Julii, repulse Britons off the mainland continent, is it better to trade with them, and the Germans? Seems much less clear, you gain less financially (your ports can trade southwards), and their gain in financial strength is likely to be spent on a re-invasion attempt.

Just wondering, what factors everyone finds important in these decisions? In past I've tended to try and trade, for wealth generation reasons. Yet actually, keeping barbarians poor, and launching a punitive raid after transgressions, sacking and destroying their developments might be a more effective pacification strategy, as Alliances are only aggressive in nature, rather than about securing borders through neighbourly relations.