On January 21, 2017, the day after Donald J. Trump's inauguration, more than three million marchers of all ages and walks of life took to the streets as part of the largest protest in American history. In red states and blue states, in small towns and major urban centers, from Boise to Boston, Bangkok to Buenos Aires, people from eighty-two countries -- on all seven continents -- rose up in solidarity to voice a common message: Hear our voice. It...