Three other approaches to ticking off the AI:
-- try to influence flip several of their planets: build influence based starbases close to some of their border worlds, especially larger more valuable ones, and keep upgrading. Eventually, the AI will notice and start asking you to remove them.
-- loom: build a number of warships and park them (using the "sentry" or "guard" function) next to the AI's planets. Eventually, the AI will ask you to remove them too.
-- delay military production: If you wait to start actually building ships, the AI will see you as "weak", and start demanding tribute and techs from you, eventually declaring war. Be sure to notice: I mean only to delay building the ships: you should keep up the pace of military research, and make sure that you have planets capable of rapid productions, so that you can start churning out ships when war does come.
All of these aren't really necessary at challenging or above. At the harder levels, and with aggression turned up, I usually don't have any problems getting the AI angry enough to come after me.
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