The next page of the guide to Anno 1800 describes how diplomacy works in the game.
In the lower left corner you will find the diplomacy icon. There you will find information about who you currently have an alliance with, with whom you trade or have peaceful relations, and who is your enemy. It is worth checking the situation from time to time, as your actions can effectively flatter / annoy your neighbors on the map. When you click on the portrait of other players, you will learn how to compare your economy and military potential.
You can take several interacting actions with other factions. You can, for example, compliment them, insult them, or give them gold to improve contacts. There is also the option to offer an alliance, suspend war, or to start a trading cooperation. It all depends on your approach and relationship with other factions.
Each faction works a little differently and various things improve / worsen relationships with them. For example, Jean La Fortune can positively understand the expansion of your fleet and the construction of defensive towers. On the other hand, Princess Qing may feel threatened by your military aspirations. A good way to improve relationships is basically trading, which is very good at building relationships with others.