How Did My Stairs Become Unlevel? 

Stairs can become unlevel due to a plethora of reasons. In most cases, the uneven stairs are caused by wider structural issues in your home. However, if the steps are outside, it could be an issue with soil saturation. The problem is most likely caused by the soil beneath the steps if they are outside of your property. Extremely expansive soils, such as clay, can become unstable over time. Their moisture content causes them to shrink and grow. This causes an uneven surface for your stairs to rest on, which will inevitably cause them to become uneven.