During the time when your home was being built, the foundation extended a few inches about ground level. Since then, other people who owned the home before you may have added landscaping, patios, porches, sidewalks, etc., and this can make it easier for water to leak down and over the top of the foundation. Additionally, if there are low-lying areas on the lawn that do not have proper drainage, water will build up in deep dips when it rains or when there is melting snow on the property.
Eventually, all of this moisture in the soil is going to find its way into the area beneath your home. This can happen via wall or floor cracks, through a weak window seal, or even over the top of the foundation itself - depending on the severity of the problem.
Grading issues don't just involve moisture lying stagnant in the basement, but it can also cause the soil around your foundation to swell up.
For proper yard drainage, we recommend having a reliable system like the NDS EZ Flow installed. The EZ Flow is a gravel free french drain system that is easy to install, and effective in diverting water away from your home.