The main effect of muckraker Upton Sinclair's The Jungle was it

increased environmental awareness and decreased pollution

brought about reform of the meatpacking industry by the government creating and enforcing laws to make it safer and cleaner

encouraged the government to break up the oil monopoly and regulate the steel industry

forced the federal government to establish national forests

The answer is that it brought about reform of the meatpacking industry by the government creating and enforcing laws to make it safer and cleaner. The Jungle is a novel written by Upton Sinclair in the year 1906 which is about the health violations and unsanitary conditions of the meatpacking of the American Industry. This was an issue in the 20th century which became a downfall of some industry in the country.

Answer is: brought about reform of the meatpacking industry by the government creating and enforcing laws to make it safer and cleaner.

The Jungle is a 1906 novel written by Upton Sinclair. He wrote about health violations and unsanitary conditions in the American meatpacking industry during the early 20th century.