If you no longer want to be a member of a particular city's tribe, select Tribe & Alliances under the 3 dot Manage menu, then select the Trade Alliances tab. Find the city you want to leave, click/tap the “Bow Out" link, then click/tap the Bow Out button. Once you bow out you will no longer receive updates on their activity.
The city is not notified that you are no longer their tribe member so feelings don't get hurt.
Well Street
If you no longer want to be a member of a particular city's tribe, select Tribe & Alliances under the 3 dot Manage menu, then select the Trade Alliances tab. Find the city you want to leave, click/tap the “Bow Out" link, then click/tap the Bow Out button. Once you bow out you will no longer receive updates on their activity.
The city is not notified that you are no longer their tribe member so feelings don't get hurt.