Perhaps the poverty he endured as an immigrant led Jacob Riis to his life's work as a reformer. In 1877 he joined the staff of the New York Tribune as a police reporter and was drawn to stories involving the disadvantaged. Massive immigration from southern and eastern Europe had a profound effect on American cities such as New York, where poverty and squalor were endemic. Like many reformers of this era, he viewed these immigrants-along with Asians and blacks-as inferior; nonetheless, he voiced his outrage over their misery in his masterpiece, How the Other Half Lives (1890). Setting the foundations for modern photojournalism, Riis used technical innovations to photograph the dark interiors of tenements. He formed a close friendship with Theodore Roosevelt, who, as police commissioner and later as governor of the state, worked with Riis to improve tenement conditions.