For Imperialism see:
John Hobson Imperialism (1902)
Max Weber The Protestant Ethic and the Spirit of Capitalism
Statistics on the Extent of Europea Colonialism
Empire and Imperialism: Europe - Gale Group
For Emigration see:
European Emigration to America
Eastern European Immigration - gale group
Emigration Across the Atlantic
Leaving Europe- A new Life in America - DPLA
American Perspective -
History of Immigration 1850 - Present
For a contemporary review on the impact of Emigration on Europe see: European Migration Report