Soil moisture change is the dominant cause. Expansive clay swells when wet and shrinks when dry, and the cycle moves whatever sits on it. Poor drainage, large trees close to the house, and plumbing leaks all amplify it.
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Foundations rarely move because the concrete failed. They move because the ground under them changed volume, and in this region that is mostly about water. Greater Cincinnati sits on glacial till over Ordovician limestone and shale, with clay-rich soils that hold water and hillside slopes that concentrate it. Soil that expands when it takes on water and contracts when it dries applies and removes support cyclically, and the parts of a foundation that experience the cycle differently move relative to each other. That differential is what cracks walls and racks door frames. What amplifies it. Drainage that concentrates water at one part of the foundation: a disconnected downspout, grading that has settled and now falls toward the house, a driveway pitched inward. Large trees close to the structure, which withdraw substantial moisture from the soil within their root zone during dry months and create localized shrinkage on one side of the house. Plumbing leaks under a slab, which do the opposite by saturating one area continuously. And drought followed by heavy rain, which is the fastest cycle of all and the one that produces a wave of new cracks in a single season. What you can actually control. Keep moisture uniform rather than maximizing or minimizing it. That means downspouts discharging well away from the house, grading that falls away, and consistency: a foundation that stays uniformly moist moves less than one that swings between saturated and bone dry. In a severe drought, slow deep watering at the foundation perimeter is a legitimate practice for slab-on-grade homes in expansive soils, and it should be even rather than heavy in one spot. What to check before assuming soil. A suspected under-slab plumbing leak can be tested, and finding one changes the repair entirely, because fixing the leak addresses the cause rather than the symptom.