Most retaining walls that lean, bulge, or crack fail for the same reason: water. Soil behind a wall gets much heavier when it's saturated, and in Kansas it also freezes and expands. A wall that wasn't built to let that water out is fighting pressure it was never designed to hold.
It starts with the base. The trench is dug down to firm soil and filled with compacted gravel so the first course sits on something that won't settle. That first course gets set perfectly level, because every mistake at the bottom shows up bigger at the top.
Behind the wall, clean drainage stone goes in instead of the dirt that came out, with a perforated drain pipe at the bottom to carry water out the ends. That stone lets water drop and drain away rather than build up against the back of the block.
Taller walls need more. Block walls typically step back slightly with each course, and walls holding back a lot of soil may need geogrid reinforcement layered into the backfill. Walls above a certain height can also require engineering or a permit, so check with your city before a big project.
Built right, a block or stone wall can turn a slope into a usable flat bed or yard and stop erosion for decades. Built wrong, it's a project you end up paying for twice.