By World War One, journalism had become a way to investigate corruption and a platform for promoting change. This led to massive change in legislation and the eventual break up of Standard Oil and the passage of the Pure Food and Drug Act (1906). Some prominent muckrakers include: Nellie Bly, Charles E. Russell, Lincoln Steffens and Upton Sinclair.
For more milestones in journalism, see:
Source: Edd. Applegate, Journalistic Advocates and Muckrakers : Three Centuries of Crusading Writers (Jefferson: McFarland, 1997).
Source: Ann Bausum, Mauckrakers: How Ida Tarbell, Upton Sinclair, and Lincoln Steffens Helped Expose Scandal, Inspire Reform, and Invent Investigative Journalism (Washington D.C.: National Geographic, 2007).
Source: Anthony R. Fellow, American Media History (Boston: Wadsworth, 2005), 175-209.
Source: Louis Filler, The Muckrakers (Stanford: Stanford University Press, 1968).