Poverty is the underlying cause of all homelessness. Structural changes within the American economy have had a profound impact on societies "bottom segment." No, homelessness is not caused by mental illness, addictions, or unemployment.
Gender inequality is a cause of poverty for women in poor countries. There's no country in the world in which women are treated as equals to men. Patriarchal cultures are those in which men control the household, in situations of poverty women eat after the men.
National Coalition for the Homeless: A national advocacy network committed to "ending homelessness". Provides facts about homelessness, references to research materials, a directory to homeless/housing organizations, the NCH newsletter and calendar, and information about legislation and policy.