What was trust-busting
In the late nineteenth and early twentieth century, industrialization, urbanization, and immigration transformed the United States. Twenty-six million immigrants arrived in the U.S. between 1880 and 1920. Many of these new immigrants settled in America's cities, which became extraordinarily crowded. Industrialization grew rapidly after the Civil War until, by 1894, the United States' industrial output was larger than the output of its rivals: Britain, Germany, and France. Enormous new business corporations, such as U.S. Steel and Standard Oil, gained tremendous power in the American economy and in politics. Many Progressives were determined to curb the power of these business monopolies.
Progressivism was a mixture of religious and secular impulses. Some progressives believed in the Social Gospel, a theological movement that suggested that Christians ought to save society, not individual souls. Many progressives also accepted the new influence of social science. They were impressed that social scientists could study social problems and find solutions for those problems.
At the national level, progressivism began with the presidency of Theodore Roosevelt, who became president upon the assassination of William McKinley in 1901. Roosevelt became famous for trust-busting. This meant the use of the power of the federal government to break up trusts, corporations that had gained monopoly power in their line of business. Roosevelt enforced the Sherman Anti-Trust Act (1890), which outlawed combinations "in restraint of trade. In 1904, the administration succeeded in breaking up the Northern Securities Corporation, which controlled railroads in the Northwest. Most famously, the Roosevelt administration broke up John D. Rockefeller's Standard Oil company, which dominated petroleum production in the U.S. After years of effort, the government finally split Standard Oil into several separate companies in 1911 (after Roosevelt had left office). Roosevelt also signed the Hepburn Act (1906), which regulated railroad freight rates. Roosevelt's term was also notable for his interest in conserving America's natural resources. He protected millions of acres of land by creating new national parks and forests.