Advancements are a way to reflect mechanic differences between Nations. An Advancement can be taken multiple times up to a maximum as determined by the current Era. You can make up your own, but here’s a few examples that you can possibly use:
[Terrain] Agriculture – Choose a Terrain Type. The Power Cost of expanding into the chosen Terrain Type is reduced by 1 as long as it is unoccupied.
Defensive Warfare – The Power Cost to expand into your Territory is increased by 1.
Offensive Warfare – The Power Cost to expand into the Territory of other Nations is decreased by 1.
Science Focus – Decrease the Power Cost of adjusting Advancements by 1.
Progressive – Decrease the Power Cost of Adjusting National Qualities by 1.