system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is Visa/Mastercard and why do all the banks use their cards?
gpt
Both Visa and MasterCard started off as a form of cooperative owned by banks and other financial institutions. Both have now floated as independent companies.  They built worldwide networks to support payment processing from just about every retailer. That's something that would have been absolutely insanely expensive for each bank to do on their own. Also imagine how crazy the tills would be if each bank had a terminal to process payments at the till!