The best evidence to support the statement that in the late 1800s a law made it easier for magazine companies to do business is:
"This was a boom time for magazine publishing, owing part to the developments in offset printing technology as well as to the Postal Act of 1879, which had granted magazines discounted mailing rates."
This statement directly links the Postal Act of 1879 to the increased success of magazine publishing, indicating that the law contributed to making it easier for magazine companies to operate.