Answer
One factor leading to more income inequality is that of an increase of human capital. Those with higher incomes are more likely to have additional education and/or training in their industry of work (compared to those with lower incomes).
Work Step by Step
Another factor leading to more income inequality is that of an increase of unskilled labor in other countries. With an increase of unskilled labor in other countries (and at lower wage levels), demand for domestic unskilled labor decreases. In turn, the domestic unskilled laborers have lower incomes (and more income inequality).
