History and Catholic Social Thought

Next week, the readings for my "Catholic Social Thought" class are about the Tradition's historical backdrop and context.  So, there's Michael Schuck's essay on Catholic Social Thought from 1740-1890; Russell Hittinger's contribution to the Witte & Alexander volume, "The Teachings of Modern Christianity on Law, Politics, and Human Nature"; and some stuff on the rise of nationalism in the later 19th c., including in the United States, and the Church's reactions to it.

So, here's a question ... what developments, ideas, events, or persons strike you as particularly important, and particularly worth emphasizing, if one is trying to understand both (a) why the content of the Tradition is what it is (b) what, considered in the light of the Tradition, is most salient about our own time and context?