This is a unity empire quest. Empire quests are activated in the campaign automatically or in a scenario by selecting the 'Empire quest' checkbox under 'advanced setup' and 'gameflow' as you set up the game.
Empire Quests can be viewed in game by bringing up the radial menu with the Y button and selecting "Objectives".
To Unlock The Unifier:
- Maintain an alliance for 20 consecutive turns
Rewards (For being first player to finish):
- 200 Energy
Complete the Diplomat
- Sign a non-agression pact with another player
- Maintain a peaceful relationship with another player for 10 consecutive turns