Most foundation problems can be attributed to water. In most of Iowa we have expansive clay soil that is highly influenced by the amount of water that's in it. Your home has been subject to the crazy Iowa weather patterns from the day it was built. From months and months with no rain to 10 inches in one day to -20° your home has seen it all. Below is a more detailed explanation of the different ways water will affect your foundation
The freezing and thawing cycles that destroys roads, sidewalks, and parking lots is also attacking your foundation causing flexing against the wall.
Soil too Dry
When the soil becomes saturated it can lose the ability to hold the weight of the home. Water can also wash out and erode the soil creating voids causing the foundation to sink
Backfilled soil around the foundation is looser than the natural soil, meaning it's more porous than the surrounding area and collects much more water. Water is heavy and can start to push against your wall causing damage
Soil too Wet
When the soil dries out around your foundation, the house will settle down, meaning the pressure against your wall decreases dramatically and the soil shrinks.
Where clay soils contain trees the problem is more severe. Trees and heavy vegetation draw a considerable amount of water from the ground during the growing season. A mature tree can take up as much as 250 gallons of water per week. In long hot summers with little or no rainfall the tree will continue to draw moisture out of the ground and the clay will shrink. If your house is sited near individual or groups of trees serious cracking in the walls can occur as a result of ground movement.
Tree roots can greatly damage foundation walls, swelling against the foundation of a house as they grow and pushing against the walls. They can also work their way into cracks and gaps in the walls and move underneath the foundation, pushing upwards on the house and causing the house to settle poorly as the earth dries
Concrete Driveway or Patio
Concrete driveways and patios sometimes will sink over time. If they were built right next to the foundation that added pressure can damage your foundation wall