I initially thought having something like cards you could play at fixed intervals would be cool, that influence how your empire behaves (like: +1 growth in deserts, -1 battle cost, etc). But ended up just sticking to what I got working well half way into the jam. And more interesting things felt like they'd require a lot of balancing to work.
The square structures are walled bases, the white pixel is the actual base. They produce resources which allow your empire to do more per tick.
Thanks for playing and the feedback!