Columbia subject headings:
Catholic Church--Europe--History--20th century.
Europe--Church history--20th century.
Harvard subject headings:
Catholic Church--Europe--History--20th century.
Christian socialism
Church and social problems--Europe--Catholic Church.
Labor--Europe--Religious aspects--Christianity.
Labor--Religious aspects--Christianity--Europe.
Socialism and Christianity--Catholic Church.
Princeton subject headings:
Catholic Church--Europe--History--20th century.
Christian socialism.
Church and social problems--Europe--Catholic Church.
Labor--Religious aspects--Christianity--Europe.
Socialism and Christianity--Catholic Church.