Finance, Forex and Investments

How does cutting financial institutions that work with Iran's central bank effect the US financial system?

Sanctions signed into law by U.S. President Barack Obama on New Year's Eve would cut financial institutions that work with Iran's central bank off from the U.S. financial system, blocking the main path for Iran to receive payments for its crude. So I read this and I would like to understand why Iran does not receive the money directly from the others countries? How is the money routed to Iran, through the US? How does it all work and why would cutting off other countries block Iran from getting payments?

Public Comments

1. I think that US banks have offices all over the world, so this will limit Iran's ability to receive payment.
2. US $ is major source of calculation in most of the business and the main link is if US banks rejects iran's central banks the value for iran currency goes low and they cannot import any item with same value as the value will increase and it causes inflection in their economic budget.
3. essentially, its economic Warfare, which means the troops will be marching.