A very important concept in Dark Forest is "Energy", which represents the planet's energy, the planet's energy will increase over time until it reaches the planet's energy limit, by sending energy can attack to occupy other planets or enhance their own planets, around the core concept of energy, you can start a very exciting interstellar battle. In fact, in Dark Forest's underlying contract, Energy is actually represented by Population, but in the UI, Energy is used instead, so isn't it a bit more understandable?