After some long hours I finally managed to get tribal expansion under control:

It turns out there were many mini bugs still hiding within the migration code (Some of these bugs I had introduced myself just the weekend before). But all that seems to be handled now. So this weekend I had time to continue working on aggression, which now has a more noticeable effect. You can see a good example on the gif above, near the bottom left corner, a blue tribe splits into two, then proceeds to start swallowing the newly birthed red tribe, before splitting once more and losing momentum.

There are still a bunch of problems with aggression. It doesn't seem to motivate any kind of expansion most of the time. This appears to be due to most tribes having very similar levels of aggression, which means that on only on rare occasions a tribe will be able to overpower their neighbors. There are a few things I will do to solve this, like introducing events that will make some tribes much more aggressive (or vice-versa) than their neighbors. I will also add a warfare knowledge attribute which will give bonuses to aggressive tribes over time. Though neither of those solutions won't possibly be enough to make aggression interesting enough yet. More work will be needed in future updates.

There's a bigger issue that I want to tackle next though. Tribes are splitting way too frequently into very small, one-celled tribes. This is mostly due to administrative cost calculations, which are used to decide when to trigger clan and tribe splitting events, going bad very quickly. I'll probably spend one weekend on two trying to fix those calculations before I continue working on tribal aggression.

Finally, next weekend I'll start a week long vacation trip. So there might not be an update until two weeks from now. Though I might take a quick break during my trip just to post a quick update...