In his new book, “Epidemics and Society: From the Black Death to the Present,” Frank M. Snowden, a professor emeritus of history and the history of medicine at Yale, examines the ways in which disease outbreaks have shaped politics, crushed revolutions, and entrenched racial and economic discrimination. Epidemics have also altered the societies they have spread through, affecting personal relationships, the work of artists and intellectuals, and the man-made and natural environments. Gigantic in scope, stretching across centuries and continents, Snowden’s account seeks to explain, too, the ways in which social structures have allowed diseases to flourish. “Epidemic diseases are not random events that afflict societies capriciously and without warning,” he writes. “On the contrary, every society produces its own specific vulnerabilities. To study them is to understand that society’s structure, its standard of living, and its political priorities.”