Why there arises a need for System testing when the component and Integration level testing is already performed?

While we were into Component and integration testing our focus was confined to modules. We were performing specification based or business-based testing. In system testing we test the behavior of the whole system based on risks, requirements, business processes, use cases or other high-level description of system behavior, interaction with the operating system and system resources. This is most often the final test to verify that the system to be delivered meets the specification and its intended purpose. It also investigates the application both w.r.t functional and non-functional requirements.

The important thing about system testing is that it requires controlled test environment, control to s/w version, test hardware and test data.