Quoting JDoe1013, reply 41https://www.sinsofasolarempire.com/upgraderebellion.aspx
IF I purchase this here, I get diplomacy as well?
The options listed are based on what you have registered with us. If you don't own Entrenchment or Diplomacy, you'll be provided with an option to buy those now in addition to Rebellion in case you want to get in on some more advanced action right away.
Now, if someone who's never owned a Sins game before buys Rebellion, will they be able to load up Vanilla, Entrenchment, and Diplomacy, or will they only be able to load Rebellion? (It sounds crazy, but some Rebellion purchasers might want to work their way up from Vanilla through Entrenchment and Diplomacy to Rebellion in order to reduce the complexity as they learn the game.)
Just wondering because my general advice to newbies is to first learn Vanilla, and to then incrementally move up to Entrenchment and then Diplomacy.