Women in the US make about 75 cents on the dollar compared to men. Being a primary caregiver is hard on your earning potential, and women tend to be primary caregivers. They engage in more part time work than men, which explains part of the gap, and there are differences in education (fewer women in engineering or business). However, some of the difference is likely discrimination.
It turns out that the wage gap is even more a problem in German than in the US, and than in most Western European nations. The New York Times has an article.