"They are coming, will we be ready?" ::looks at the size of the Scourge:: I'm guessing... No. Unless some very clever scripting and mods are going to come into being...
I know how Paradox could fix the Prethoryn swarm... 1) Fix all glitches involving their unit spawning. I've had the prethoryn show up, invade a planet, fail, lose all their planet-invading units, and NEVER SPAWN THEM AGAIN. They infested zero worlds, and just sat there until I destroyed them 20 years later. 2) If all Prethoryn queens are dead, spawn 1 or 2 new ones every 10 years to make sure the galaxy can't just passively "wait out" the Prethoryn.
ASpec to know the reason why they don't want to trade with you, you have to look at the nummber. The reason is there attidute towards you. If they are neutral there is an 50% chance they will trade with you. The chance will be better or worse depending on the attitude. The % you see to the right of the number is the chance you have for a trade deal. Hopes this helps.
It's not their attitude. That number is the base trade willingness, which is based on their personality. It does not change. Attitude can increase or decrease likelihood to accept trade, but the little number is constant.
