Many countries during world war II started colonizing planets in search of resources and new recruits.
At the end of world war 2 a nuclear war occurred, destroying earth in process.
Countries on their planets started developing advanced technology.
Even after wwII every planet and country is preparing itself to war and the galaxy isn’t a safe place.
Filled with slave hunting races, space pirates even planet eating monsters.
However many inteligent races were discovered. Some of thrm peacefull, others not so much.
Oil is history. Now various crystals are sources of energy on planets.