Which government institution was founded to combat counterfeiting of US currency after the Civil War?

The Secret Service was established in 1865 primarily to combat the rampant counterfeiting of U.S. currency that occurred following the Civil War. At that time, it is estimated that one-third of all currency in circulation was counterfeit, which significantly undermined the integrity of the nation's economy. The Secret Service initially focused on financial crimes and counterfeiting before expanding its role to include protection and security functions, such as safeguarding the President and other high-profile individuals.

The other institutions listed have different primary functions. The FBI focuses on general federal law enforcement, including investigations of terrorism and organized crime. The Treasury Department manages the country's finances and the issuance of currency but was not specifically founded to address counterfeiting. The Bureau of Printing and Engraving is responsible for printing U.S. currency but was created after the Secret Service and does not have law enforcement authority. The Secret Service stands out as the agency specifically created with counterfeiting as its initial mission, making it the correct choice.