Wage inequality is really a sign of a deeper problem; basically it reflects an economic system that is not growing rapidly enough to satisfy everyone. In a finite world, it is easy for an economy to grow rapidly at first. In the early days, there are enough resources, such as land, fresh water, and metals, for each person to get a reasonable-sized amount. Each would-be farmer can obtain as much land as he thinks he can work with; fresh water is readily available virtually for free; and goods made with metals, such as cars, are not expensive. There are many jobs available, and wages for most people are fairly similar.
As population grows, and as resources degrade, the situation changes. It is still possible to grow enough food, but it takes large farms, with expensive equipment (but very few actual workers) to produce that food. It is possible to produce enough water, but it takes high-tech equipment and a handful of workers who know how to use the high-tech equipment. Metals suddenly need to be lighter and stronger and have other characteristics for the high tech industry, thus requiring more advanced products. International trade becomes more important to be able to get the correct mix of materials for the advanced products needed to operate the high-tech economy.
With these changes, the economic system that previously provided many jobs for those with limited training (often providing on-the-job training, if necessary) gradually became a system that provides a relatively small number of high-paying jobs, together with many low-paying jobs. In the United States, the change started happening in 1981, and has gotten worse recently.