Let the ruling classes tremble at a Communistic revolution. The proletarians [common people] have nothing to lose but their chains. They have a world to win.

Working men of all countries unite!

—Karl Marx and Friedrich Engels, Manifesto of the Communist Party, 1848

The excerpt suggests that the authors saw historical events as results of
A.
social conflict.
B.
military victories.
C.
industrial regulation.
D.
international diplomacy.