ZeroTwentyThree is correct, KoW has several human centric armies, and each one can represent different aspects of the Empire.
KoW is the more vanilla one, perfect for exemple for an Altdorf army with lots of state troops, knights, classic war engines and the like (also note that the beast of war can make a very good War wagon, and a decent steam tank)
Basilea is your religious army, with warrior priest, flagellants, and religious knights orders, and if you want to use Elohis (angels) the starter box from Age of Sigmar will provide you with flying sigmarines (sorry, stormcast eternal) that will be perfect for the role of daemons of Sigmar
The league fo Rhordia has the more exotic options, it can be used for a nuln army with exotic war engines (including a steam tank), as well as for a knightly order with a griffon theme (the Aralez riders are your demigriffons), and you also have a shrine that can use the models for the luminark/war altar
And of course with the allies rules you can mix if you really want an army with options from differents lists.
In theory you might also use the Brotherhood as it is another human list with knights, but this one is more suited for our Bretonnian cousins.
Also, not all units in KoW have an equivalent in Warhammer 8th edition, but some entries might correspond to things like some of the old Dogs of War mercenaries units, and others might be used to represent other elements from the fluff.
For exemple you might want to use the berserkers as Ulric themed fanatics, some of the light cavalry might be used for Kislev units, the ballista despite not being an option in the Warhammer list certainly exist in some remote areas of the empire with less gunpowder access (a roman scorpio movel will be perfect).