So, since practically the 1880s or so, the USA was very industrialised as well as being very large. It got many immigrants, it had many resources, it was protected by the ceans and the British, the only ones who could get to them outside of France and Mexico, were cintent to be friends. It had massive agricultural capabilities... basically OTL is an Ameriwank economically.
It's not really fair; America is both large and has much industry. Since 1900 it has been uber-dominant.
Russia, perhaps, could be similar but it had a host of other problems and doesn't have as much industry. It's population is smaller too.
So, let's have an America that has industry, but not too much, around the time of 1900 and mostly throughout the 20th century. It primarily exports resources and agriculture like the rest of the New World. It has less population and is more thinly settled. Industry could be behind Russia.
How could this come about? What are the ramifications? How much more important does Europe stay?
Note: Yes, it has massive amounts of coal and such. But so did Russia! So, it's not ASB.
(Waits for Ameriwank brigade to start massive moaning and calling ASB).