Our social systems are a product of the interactions between ourselves and those around us. Human nature dictates what is involved in these interactions. Therefore, one could argue that all social systems are products of human nature.
Inequality is inherent in any biological system. Some organisms in a system will have greater fitness (ability to thrive and reproduce) than others. In a capitalist system, the requirements for fitness are quite different from what you would find in a communal tribal setting, but hierarchy can be found in either setting. There will always be leaders, those who wish to be leaders, and everyone else. In order to increase their own fitness, leaders may be oppressive.
The most important thing is that a culture institutes checks on the leaders to prevent them from becoming oppressive.