Kingdom adventure is non-magical fantasy where nothing happens in the book that couldn’t happen in our world (no talking animals, fantasy creatures, fantasy races, etc) but the realm of the story is completely made-up and does not fit in any country, time period, or historical era of our world. The genre usually places the emphasis on the adventure.
Examples would be Ranger’s Apprentice (besides the first two books) by John Flanagan, the Brotherband series also by John Flanagan, and the Ascendance series by Jennifer A. Nielsen.
The Blades of Acktar is a Christian Fantasy/Kingdom Adventure series filled with adventure and danger. In a Medieval meets American West setting, an assassin, Third Blade Leith Torren, must decide to either follow his king’s orders or risk his own life to do what is right.