Simplify the following text for a Grade 12 native English-speaking person.
Original: From early 1980s until the early 1990s , American Express was known for cutting its merchant fees ( also known as a `` discount rate '' ) to merchants and restaurants if they accepted only American Express and no other credit or charge cards .
Simplified: From early 1980s until the early 1990s , American Express offered merchants and restaurants a discount if they accepted only American Express and no other credit or charge cards .