The only power remotely capable of economically beating the US during the 19th century was Britain. True; but (according to Bairoch via Kennedy) the relatives shares of world manufacturing output were 4.3 percent (UK) to .8 percent (US) in 1800, 9.5 to 2.4 in 1830, 19.9 to 7.2 in 1860, 22.9 to 14.7 in 1880, and 18.5 to 23.6 in 1900; the US was number two in the world by 1880, after passing France sometime between 1860 (7.9 percent) and 1880 (Germany was third, at 8.5); the path is pretty clear.
The trouble with these stats are they don't show who invested in the countries to produce the increase in manufacturing output.
By far the largest investor in the US was the UK, outstripping home investment until the late 1890's and coming a close second right up until the outbreak of WWI.
Without this investment the US would have stayed a mainly an agrarian society and even more inwardly looking than it was.