The basic idea behind social disorganization theory is that some communities experience high rates of deviance (including crime) because they are not sufficiently organized. This means that they are not capable of exerting social control over their members.
Social disorganization theory holds that a community must have solidarity, cohesion, and integration among its members in order to keep from experiencing serious problems. The idea of solidarity is that the majority of the residents of the community must agree on a set of values. If the community does not agree that crime is bad, it will have a hard time preventing crime from occurring. Integration exists if the various people in the community interact often and cohesion exists if they have strong bonds with one another.
These things are important because they allow a community to maintain social control over its members. When members agree on values and feel closely tied to one another they will care about their values and will try to force everyone in the community to live by those values. If these characteristics are absent, the community is said to be disorganized. Its members will not enforce a set of values and the community will be more likely to have many members who will engage in crime and other deviant behaviors.