A system is always contained within an other system.
Ultimately, seeking systems's wholes and the whole of systems leads to the One, or the Whole.
The whole is much more than the sum of its (identified) elements.
One way of looking is from the system up, towards "wholer systems.
An other way of looking is from a system down. This requires functional thinking: what are the functions of the system, and how does it differentiate itself to perform these functions?
See also: Holism.