Visa Inc.

Visa isn't the biggest company in global commerce - it's the mechanism that makes global commerce work. Processing $14 trillion annually across 200+ billion transactions, Visa connects 15,000 financial institutions, 100+ million merchants, and 4+ billion cardholders. The company doesn't issue cards or acquire merchants - it's the network connecting issuers and acquirers globally. Remove Visa, and e-commerce doesn't slow down; it stops. This is what keystone species look like in business.

The architecture creates self-reinforcing network effects. Every additional issuer makes Visa more valuable to merchants; every additional merchant makes it more valuable to issuers. Even direct competitors share the infrastructure - banks that compete for customers pay 1-3% transaction fees because building independent networks costs more than the fees. Visa maintains ~50% operating margins in stable duopoly with Mastercard, where multi-homing is costless for merchants and consumers. The companies compete on value-added services (fraud detection, analytics) rather than race-to-bottom pricing, because regulatory constraints and shared standards (EMV chips, contactless, tokenization) prevent destructive warfare.

But keystone power creates systemic vulnerability. A 2018 outage in Europe froze millions of transactions for hours. The structural position that makes Visa indispensable - being the connecting mechanism for global payments - also makes it a single point of failure. The lesson for business: keystone positions provide extraordinary leverage and margins, but also attract regulation, disruption attempts, and catastrophic-if-you-fail risk. You can't be the thing that connects everything without becoming the thing that breaks everything when you fail.