Just realized you've been playing tiny. I don't get scouts on tiny or small.
should one go for dreadnoughts and build AMM to bump military superiority in the mid-game
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Okay. I've seen some disagreement on this. My feeling is that you should only build a military if you're about to use it, otherwise it's just wasted maintanence, especially since the tech pace is so fast that your ships will very quickly be obsolete, and since the AI will almost always be able to outproduce you.
The other comment would be that you sometimes need to enter these wars that you start, when it looks like one of the AIs will become too dominant--since you're playing tiny, taking out a single star system should be enough to shift the balance of power. You can do this even with a vastly inferior fleet, since the AI doesn't defend its worlds adequately--I've taken out enemies with Dreadnaught Technology while using battle hammers--you just have to take the AI by surprise.
Also, you may wish to cease trading techs with the dominant AI, in order to help the other ones keep up.