Concrete basements and foundations are going to crack. The cause and severity dictates what type of repair is required. There are several reasons why concrete cracks.
As concrete cures the moisture evaporates and this evaporation can cause the concrete to shrink. Shrinkage is a common factor in all concrete and oftentimes this shrinkage causes cracking. Overtime the backfill around your foundation compacts and settles. This settlement can affect the foundation as well as the earth under the house settling from the weight of the house. Foundation settling can cause cracking. Horizontal cracks in a foundation are usually caused by soil pressure. Most soil movement is due to expansive soil. As the soil absorbs ground water it expands. As soil expands, it moves and swells. This movement and expansion causes unbalances pressure on the foundation. This pressure pushes on one side of the foundation causing cracking.
No crack is a good crack and should be repaired immediately.
the solution: polyurethane injections or sealants
Sealants are used in areas where there is expansion and contraction. The elasticity of sealants make them flexible enough to maintain a watertight seal with the expansion and contraction that comes along with extreme temperature and soil moisture changes.