Societal forces influence management because societal forces change people and technology. Since management has a great deal to do with these things, they change management theory and practice as well.
For example, in the early 1900s, workers were cheap and not very respected and America was industrializing rapidly. Therefore, Taylorism was a very popular management style. It treated workers like the new machinery, trying to break everything they did down into steps that could be made more rational and efficient.
Today, the major (relatively) new force is information technology. People are used to using their computer to help them and management is no different. With quantitative management, managers try to use information technology to rationalize the management process.
Societal changes change the way people think and the technological environment in which they think. These factors lead to changes in management theory and behavior.