An example of accumulated U.S. firm advantages that provide economies of scale and network effects that in effect, become self-perpetuating across many market segments.
Citibank has a global payments markets infrastructure, to allow for international trade and foreign business transactions, across thousands of foreign banks, and hundreds of currencies - it is thus the go-to bank for any business that needs to move money across borders. Anyone else that attempts to compete would need to convince businesses to move to a network without any scale and would need to convince thousands of banks globally to build an API around them when they already have an API with Citi and they would need to convince investment banks to hedge FX risk with them using futures/forwards/swaps despite lower and less volumes. Citi’s incumbent position allows it to have massive scale (thousands of banks, hundreds of currencies, best in class risk management) and network effects (anyone moving money across borders defaults to Citi; all upstart banks use Citi) and both make it very difficult for anyone else to enter. The US has tens of thousands of firms like Citi - operating in niche but important market segments that all have their own network effects and scale effects -
from network tld registration at VeriSign, operating systems and office productivity software at Microsoft, industrial gas manufacturers such as Praxair and Air Products & Chemicals, gas turbines manufactured for electrical generation from General Electric, credit and debit card transactions through Visa and MasterCard, life and property insurers (larger size means greater solvency and confidence among insureds - leading to more customers - for example, MetLife and Travelers from New York and Chubb from Chicago are just about the only insurers that sell globally), or even package couriers such as UPS and FedEx (who operate globally in a way no other courier does).