OVERVIEW FROM WIKIPEDIA:
Editor's Note: This is an area where Wikipedia falls short without substantial research into the history of the income tax system and IRS.
The Internal Revenue Service (IRS) is the revenue service for the United States federal government, which is responsible for collecting U.S. federal taxes and administering the Internal Revenue Code, the main body of the federal statutory tax law. It is an agency of the Department of the Treasury and led by the Commissioner of Internal Revenue, who is appointed to a five-year term by the President of the United States. The duties of the IRS include providing tax assistance to taxpayers; pursuing and resolving instances of erroneous or fraudulent tax filings; and overseeing various benefits programs, including the Affordable Care Act.
The IRS originates from the Commissioner of Internal Revenue, a federal office created in 1862 to assess the nation's first income tax to fund the American Civil War. The temporary measure provided over a fifth of the Union's war expenses before being allowed to expire a decade later. In 1913, the Sixteenth Amendment to the U.S. Constitution was ratified authorizing Congress to impose a tax on income, and the Bureau of Internal Revenuewas established. In 1953, the agency was renamed the Internal Revenue Service, and in subsequent decades underwent numerous reforms and reorganizations, most significantly in the 1990s.
Since its establishment, the IRS has been responsible for collecting most of the revenue needed to fund the federal government, albeit while facing periodic controversy and opposition over its methods, constitutionality, and the principle of taxation generally. In recent years the agency has struggled with budget cuts and reduced morale. As of 2018, it saw a 15 percent reduction in its workforce, including a decline of more than 25 percent of its enforcement staff. Nevertheless, during the 2017 fiscal year, the agency processed more than 245 million tax returns.