We are witnessing a moment of unprecedented political engagement and social activism. Pundits once fretted about Americans' apathy, but in the last few years we've seen uprisings and protests across the country: the growth of the Tea Party; the successful fight for a $15 minimum wage; a 21st century black freedom struggle with Black Lives Matter; Occupy Wall Street; and the grassroots networks supporting presidential candidates like Bernie Sanders.

Americans' new social movements are reshaping the idea of class struggle for the 21st century.