Why do immigrants leave their homelands?

What specifically motivated the Irish? What conditions have contributed to immigrant's efforts to re-settle in the United States?

What issues and prejudices have various immigrants face as they tried to assimilate in America? The American melting pot has been an image of hope and inclusion for more than a century. How has that image been true or false throughout U.S. history? Is the "melting pot" analogy alive today or have fears of too much change overtaken its positive history?

*** This is for an intro to diversity studies discussion board