Jacob A. Riis 
A Ten Years’ War [EPUB ebook] 

The slum is as old as civilization. Civilization implies a race, to get ahead. In a race there are usually some who for one cause or another cannot keep up, or are thrust out from among their fellows. They fall behind, and when they have been left far in the rear they lose hope and ambition, and give up. Thenceforward, if left to their own resources, they are the victims, not the masters, of their environment; and it is a bad master. They drag one another always farther down. The bad environment becomes the heredity of the next generation. Then, given the crowd, you have the slum ready-made.