Region world feature.
In the Alliance Shop you can purchase various items with the Alliance Coins that you previously earned. You can purchase something for the whole alliance as well as for yourself. The items can include resources, units, and even rubies or event emblems, if you’re lucky.
The displayed purchases in the shop are chosen randomly for every single player and get updated once per day. You can also manually update by using gold. The time period for the daily update is not affected by this. You can collect personal purchases in your task list. Alliance purchases will be added automatically to the treasury, even if it then becomes overfilled.
Alliance Coin Ranking
The Alliance Coin Ranking is not affected by the purchases. Only the total of received Alliance Coins is counted, not the currently available coins. You do not receive any coins for buying alliance resources.
The Alliance Shop does not get updated when your current alliance changes. You have to wait for the next daily update or manually update.
The received Alliance Coins are bound to the alliance, which means you can have Alliance Coins in multiple alliances. This also applies for available Alliance Coins. So if you leave and later reenter an alliance, the amount of total and available coins stays the same, regardless if you earned coins in another alliance or not.