The peace secured by the League of Nations after the Great War allowed the Twentieth Century’s greatest minds to focus on exploration rather than war. Mankind was propelled into space on the fires of atomic rockets. That they encountered offshoots of humanity on both Mars and Venus (not to mention remnants of older, stranger races) came as quite a shock. But it was only a short leap from League of Nations to League of Planets.
This second age of exploration drew the attention of extra-solar civilizations that maintained outposts beyond the Jovian orbit. Mankind’s leap into space gave them probationary status in the galactic community but it also opened them up to exploitation by technological superiors.
And so we come to Gateway, the grandest port on Mars and home to a space elevator extending upwards from the ruins of a wondrously ancient precursor spire. At this crossroads of the solar system, the League of Planets Expeditionary Force keeps the peace as smugglers, gangsters, and spies ply their trade. The Legitimate Terran (or Martian or Venusian) merchants trade abundant natural resources and unique cultural artifacts for Galactic Alliance-approved technology and trade goods. But much, much more shows up on the Black Market, with Alliance Monitors always on the lookout for contraband hyperdrive technology that would grant the upstart Humans the keys to their own destiny.