In order for you to be able to conduct faction upgrades, Captains of a specified rarity must meet certain level conditions. The Hall of Fame requires that all factions meet certain level requirements.

One of the most common reasons why players are unable to upgrade a faction is that they misread the upgrade requirement, which always refers to the rarity of your Captains.

Legendary Captains have an orange background, epic Captains have a purple one, and rare Captains have a blue background.

So, if a faction upgrade requirement reads:

Level xxx epic or legendary Captains of this faction needed: x

this means that you must getx Captains with purple or orange backgrounds to level xxx to unlock the upgrade.

Please take a look at the example below.

Here we can see that in order to level up the Resolve faction to level 106, we need to get two epic OR legendary Captains to level 290. Please note the highlightedOR. You will meet the requirement for the upgrade if:

1. You upgrade any two purple Captains from the Resolve faction to level 290. E.g., Dustan and Aurora.
2. You upgrade any two legendary Captains from the Resolve faction to level 290. E.g., Cleopatra and Ramses II.
3. You upgrade one purple AND one legendary Captain from the Resolve faction to the required level. E.g., Cleopatra and Aurora.

Leveling up Proscope and Xi Guiying won't help, as they are rare Captains.

If you can't upgrade the Hall of Fame, that means your factions don't meet the level requirement.