Your Alliance will need to upgrade its Black Sites in order to increase the amount of Serum that can be stored there, and also to be able to enhance different types of Units. Upgrading Black Sites also increases their Range (the amount of territory the Alliance controls as a result of controlling the Black Site).
Black Site upgrades require considerable Resources, which is why all Alliance Members are advised to contribute Resources.
You can track contributions to a Black Site Upgrade by tapping on the “History” tab, and then the “Contributions” sub tab.