Alliance

In Spore, you can create an alliance with any other Creature, Tribe, Civilization or empire once you have a reach a green smiley relationship with that creature, tribe, civilization or empire. In most cases, alliances can not be revoked.

See: Relation bonus for more information.

Creature stage
In Creature stage, you can ally with another species by befriending 3 members of the species. You can befriend them singing, dancing, posing or charming. Allied species can join your hunt pack, and you can also heal at their nests. If you befriend an Alpha Creature, you unlock a new part. Be careful though, most carnivores start out disliking your species. Other species will automatically be hostile towards you, for no reason.

You can also, by having strong social skills and pack members, befriend Rogues. You only need to socialize one time (sometimes two) with the Rogue to ally it. Rogues are extremely powerful (Only Epic Creatures are stronger), and to most players they are very valuable.

Tribal stage
During the Tribal stage, you must play music for other tribes at least twice in order to ally with that tribe. Use the Maracas, Wooden horns, or Didgeridoos to do this. Sometimes you may need to bring a gift (needs at least 10 food) before that if they dislike or hate you normally. Allied tribes will constantly bring gifts to you, and your relationship with them won't decrease as time passes, however, attacking them via firebombs or other non-direct attacks will lower your relationship.

Civilization stage
In the Civilization stage, giving gifts and complimenting a civilization are the simplest ways to raise your relationship. However, while taking over an civilization, you may see your relationship with another civilization quickly rise. That is because you fought their enemy, which gives a large sum of alliance relation with that civilization. Also, buying their city for a generous sum will make them more friendly with you.

Through allies, you can ask them to attack other civilizations, and at the end of the game, they will ask you if they can join your empire. This is called a Diplomatic takeover.

Space stage
There are lots of ways to be awarded a green slimey relationship. Those ways are to bring Gifts (the higher the amount of Sporebucks, the better), do missions, agree to help that Empire, trade, use the Happy Ray, place an Embassy on one of their planets, use Planet Buster on their homeworld, making a generous offer to buy their star system, terraform one or more of their planets, and defend them from Eco Disasters and attacks.

Through allies, you can add new ships to your Space Fleet and you can have them help you conquer an enemy empire. They can also teach you their philosophy. Allying with them also speeds up your progress in the Body Guard, Diplomat, Trader, Economist, Zoologist, Missionista and Eco Hero Badges.