@bearcoco
when you time travel for the first time (and maybe conquer your first planet. conquer not colonize) then the diplomacy tab will stay for good. until then the only way to get it is to upgrade inter-stellar travel.
@Nicomachus. the only reliable way is to time travel and level interstellar research to level 4. the only way pre-time travel is to level up interstellar travel. but pre- time travel the only reason for diplomacy is the galactic tournament. the early fights are good and beneficial to do but eventually they get pointless
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