The whole world, not just nature was composed of systems. He believed that by building his own manmade system (the early warning network) he could identify how all systems stabiles themselves. It was through a mechanism called "FEEDBACK". Every action we take has consequences that feed through the system, an then return to shape our future behavior in ways we cannot see. But the computers could, they had the power to analyses the true consequences of human actions, what Forrester called "FEEDBACK LOOPS"
"They (individuals) are driven in most of their actions by feedback loops;
physical systems, electrical systems, social systems, political systems, biological systems, internal medical systems, they are all fundamentally networks of feedback loops."
Transcribed from Watched over by machines of love and grace ep2