At the initial setting, change the computer's aggressive setting to "None" so that you can always form an alliance with the computer unless you annoy him/her first. There is no military victory, but victory can be achieved through the victory of culture, science and technology or space. This is the simplest method of permanent alliance.

Alliance and conquest of polis;

The polis is a small civilization that does not participate in the victorious struggle in the game and cannot form immigrants on its own. You can choose to buy the polis as an ally to get all kinds of benefits, or simply conquer it.

After the influence reaches 30, make friends with the city-state. After 60, your influence on this city-state is higher than that of other civilizations, so this city-state becomes your ally.

After friendship or alliance, the cultural city-state provides a certain culture in each round, the maritime city-state provides food for your city in each round, and the military city-state gives military units irregularly. Alliances offer more than friendship.

Extended data:

As a new city-state joining religion and commerce, the rituals of religious city-states have a small amount of faith besides money. Buying as an ally can provide confidence in every round. Commercial city as an ally will provide happiness after purchase. Jewelry and porcelain are two luxuries that only commercial city-states can have.

In each game, every military city-state will immediately acquire an army UU technology and present this unit to its allies. Hover the mouse over the word "military" in the city and state interface to see the UU type.