Answer:
The Supreme Court ruled in the case of Wabash v. Illinois (1886) that the state of Illinois could not regulate the rates charged by the Wabash Railroad because its freight traffic moved interstate, and only the federal government could regulate interstate commerce.
This was a significant decision because it limited the power of states to regulate businesses that operate across state lines. It also paved the way for the passage of the Interstate Commerce Act in 1887, which created the Interstate Commerce Commission (ICC) to regulate the railroad industry.