Loyalty from Great Generals
Great Generals give +5 Loyalty per turn to nearby cities.
The effect is active in their "aura" (the 2-tile radius around them marked with a white border).
Effect does not stack, but one Great General can provide Loyalty to multiple cities at the same time (see screenshot).
Requires Rise & Fall (if you only have Gathering Storm, that works, too).
Recommend using All (Great) Men Are Mortal to enable killing Great Generals when captured.