The work on tribal aggression continues. This weekend was spent trying to figure out how to make tribes expand more aggressively into neighboring territories. To do that, I spent some time devising a way to visualize where tribes are more likely to expand toward. Which ended with me a partial combination of the territory and region overlays which I dubbed the 'Core Regions' overlay. This overlay can display at the same time a polity's territory and the regions it considers its cores. Here's an example from a random world picked at a particular advanced date:

In the top screenshot, you can see the green tribe occupying the south part of a moderately sized region, the unoccupied parts of the region are shaded in a semi-transparent shade of the same green color to indicate that the tribe considers it part of its core. For the orange tribe which occupies the northern part of the same region, it is instead colored in semi-transparent orange. This indicates that the orange tribe also consider that region a part of its core regions. 

As long as the 'core regions' overlay is active, clicking on a particular tribe's territory will highlight all of its core regions in a color shade similar to the one assigned to the tribe. The purpose of its addition is to give me an idea on how adjacent tribes might interact with each other. If two or more tribes share a particular core region, then they have a strong incentive to compete with each other. My hope is that this will aid me in figuring ways to incite that competition and measure some sense of progress in favor of the more aggressive tribe.

The overlay is pretty much done and works pretty well, though sometimes it's hard to distinguish some regions from polity territories... In any case, I already started implementing an algorithm that hopefully will push tribes to be more aggressive with each other (when warranted). Hopefully I will have it ready by next week.