I'm amazed you haven't seen the option to get the AI to declare war. Just go to the diplomacy screen for any Malevolent race. Hit Declare War. The range for me is 3,000 to about 7,000 credits. Because you can milk the AI so much, there is plenty of cash available to do this, and you can use it to turn the galaxy into total chaos, then just mop up a target of your choosing. All I can think is that you haven't got good enough relations with Malevolent races, perhaps, but this is easy to do with a bit of an early game focus on diplomacy research/buildings.
I.e, declaration of war.
I found it depends on really two factors in this order of importance:
- status of relation between the three races (you, AI-1 and AI-2. If they hate them and they love you, no matter if they're 18th and you ask them to dow the 1st, the price won't be too heavy too pay. If they hate you and they like them, it's near impossible to get them to declare war, unless you give them all your money and half your tech three.
- relative power to the other AI. the weaker they are, the more hesitant they get. I've never seen an AI be ready to declare war for something as cheap as 3-7000. More like 30 - 70 000 and/or a bunch of techs.
Yes, I can milk the AI. It's a bit unfortunate on this side because it seems to value some techs just way too much and some others just not enough. Example: you will need to give the AI *a lot* of cash and techs to get harpoon. The next missile tech? Not so much.
Right now, when valuing techs, the AI refers to its relative value, "how many reasearch point do I need to get that tech" + some techs that are harder to trade for, like terraforming and a few military techs (not all of them).
Imho, it should add to these paramaters: "What do I gain from it" and "What does he gain from it". The AI knows what kind of military techs I'm searching for because it will adapt its ships to be more resistant to my attacks. I.e., if I attack the AI a few times with missiles, he'll switch to point defense, when I come back with beams and shields, he'll switch to shields and mass drivers for some other ships.
So, knowing that I am researching missile technology, the AI should make it harder for me to gain one more tech in this field, or support tech for a weapon he has: if the AI is very advanced in beam warfare, it should make me pay for shield suppor system. If it needs missiles because the race he's at war with is using shields, than it should be able to give me more for that missile tech and less for the mass drivers he's already using.