Here is the full list of all 26 They Are Billions achievements worth 1,000 gamerscore.
Complete all the other achievements.
Kill an Infected Giant.
Kill two Infected Giant on the same map.
Kill three Infected Giant on the same map.
Build the six wonders in your colony.
Win a Survival game (Score Factor >= 100%) without using walls, gates and towers.
Win a Survival game (Score Factor >= 100%) with just Soldiers in your army. No Attack Towers allowed
Win a Survival game (Score Factor >= 100%) with just Rangers in your army. No Attack Towers allowed.
Win a Survival game (Score Factor >= 100%) with just Snipers in your army. No Attack Towers allowed.
Win a Survival game (Score Factor >= 200%) without using Attack Towers like Ballista or Executor.
Win a Survival game (Score Factor >= 100%) with no new units trained.
Win a Survival game (Score Factor >= 100%) without pausing the game.
Win a Survival game (Score Factor >= 100%) with no casualties. No Attack Towers allowed.
Build a colony with 1.000 colonists.
Build a colony with 2.000 colonists.
Build a colony with 5.000 colonists.
Build a colony with 10.000 colonists.
Win a Survival game on Easy mode.
Win a Survival game on Accesible mode.
Win a Survival game on Challenging mode.
Win a Survival game on Brutal mode.
10.000 infected killed!
50.000 infected killed!
100.000 infected killed!
500.000 infected killed!
1 Million infected killed!