Systems thinking is a way of making sense of the complexity of the world by looking at it in terms of wholes and relationships rather than by splitting it down into its parts. It has been used as a way of exploring and developing effective action in complex contexts, enabling systems change. Systems thinking draws on and contributes to systems theory and the system sciences. See Dana Meadows, Thinking In Systems: A Primer
Systems theory#History
The term system is polysemic: Robert Hooke (1674) used it in multiple senses, in his System of the World, but also in the sense of the Ptolemaic system versus the Copernican system of the relation of the planets to the fixed stars which are cataloged in Hipparchus and Ptolemy's Star catalog. Hooke's claim was anwered in magisterial detail by Newton's (1687) Philosophiæ Naturalis Principia Mathematica, Book three, The System of the World (that is, the system of the world is a physical system).
Newton's approach, using dynamical systems continues to this day. In brief, Newton's equations (a system of equations) have methods for their solution.
By 1824 the Carnot cycle presented an engineering challenge, which was how to maintain the operating temperatures of the hot and cold working fluids of the physical plant. In 1868 James Clerk Maxwell presented a framework for, and a limited solution to the problem of controlling the rotational speed of a physical plant. Maxwell's solution echoed James Watt's for maintaining (but not enforcing) the constant speed of a physical plant (that is, Q represents a moderator, but not a governor, by Maxwell's definition).
Maxwell's approach, which linearized the equations of motion of the system, produced a tractable method of solution. Norbert Wiener identified this approach as an influence on his studies of cybernetics during World War II and Wiener even proposed treating some subsystems under investigation as black boxes. Methods for solutions of the systems of equations then become the subject of study, as in feedback control systems, in stability theory, in constraint satisfaction problems, the unification algorithm, type inference, and so forth.
