Some folks are too fond of their trees! The owners were wondering why their floor was cracking. They also had termites in the wall.
Foundation
There are 2 types of foundations generally found here in San Antonio. Slab (concrete) and Pier and Beam (wood and/or concrete posts that the wood foundation sets on top of. There is a crawl space under the house where the plumbing and electrical systems are generally located. Pier and Beam construction is generally associated with much older homes but the style is still used is some locations, especially on the coast.
Slab homes have some movement depending on the soil and drainage away from the house. Positive drainage (water draining away from the house) is necessary to help keep the slab from getting too wet underneath and making the slab move and crack.
Pier and Beam houses usually don't have very good drainage and so most of these homes have foundation movement with unlevel floors and cracks in the walls.
Adding soil around the edge of the foundation to channel water away from the foundation will help reduce foundation moement. Adding gutters can generally help reduce the movement of the foundations by also channeling water away from the foundation. Just remember, Water + Foundations = Movement.