In December 2017, in the 1.3 Update, Guns of Glory was extended with Glory Levels. This guide explains how the glory levels work.
Glory Banners can be used to upgrade the Glory Levels of Urban Buildings. Increasing the Glory Level will provide combat boosts.
It is not yet clear to me how the Glory Banners can be acquired. I will update when I find out more. In King of Avalon from the same makers the equivalent Prestige Banners can be acquired via Gathering Resources on the kingdom map, defeating Portal Monsters (Underworld Villains), defending against Fallen Knight (Red Guard Raid), and from specific packages. In Guns of Glory so far I can only confirm you can buy them in packs.
Glory levels can only be upgraded once a building reaches level 15 and the maximum glory level is the same as the maximum level of the building. Only the urban buildings have glory levels.
The amount of Glory Banners to upgrade a building level increase with higher levels (although not with each level). These requirements are not the same for all buildings, for example to upgrade to glory level 1 most buildings require 1 Glory Banner, but some require 2 and one does not require any.
Each building has its own boosts. I will extend the details page of each building with their glory boosts. All boosts are related to combat. The buildings to train troops have boosts that complement their troop type.
The value of the boost increases are the same for the first 5 levels and increase with 50% for level 6. This jump in the increase happens each 5 levels.
When clicking on any of the urban buildings there is a new Glory Level menu. Via this menu you can upgrade a building to the next glory level.
Since the Glory Banner requirements increase very fast for higher levels I am in favour of not focussing on one or a few buildings, but leveling up the glory levels of all buildings. This will give you significant boost in both attack and defense.
It is an interesting extension to have some extra boosts. In King of Avalon it was a real game changer and the non/low spenders also benefited a lot from this extension, as it was relatively easy to get these banners. In Guns of Glory I still have to figure out if you can get these banners without spending, and if so, how easy it it. If not easy or not at all, this might be a feature that will really cause a big gap between big spenders and non/low spenders
I personally find it a bit of a pity that the boosts are only related to combat, it would be interesting they were more diverse like the hero boosts.