While the book purports to deal with the USA and the British Empire, the latter is really there to serve as a kind of foil that reveals how different circumstances affected Jewish entry into the clothing trade specifically and the economy in general. While Jews in the US had a later and less auspicious start than those in the British Empire, (and by that Mendelsohn mostly means England, Australia and a few references to the West Indies), the "elaborate and geographically dispersed distribution chain" in the US laid a very effective foundation.
Through the clothing trade, Jews received schooling in essential skills essential for rapid advancement in a modern economy: "practice in petty entrepreneurship" and "sensitivity to the whims and wants of the market," but most importantly, "self-employment rather than wage labor" to facilitate a quick rise from the working class. The key to the success of Jews in the US was entrepreneurship in a field that required minimal investment of capital to start. Genius.
Mendelsohn showed clearly how specific economic behaviors and historical events informed each other. In places, there were points of momentous import that that needed greater emphasis, but that's to be forgiven. He admirably resisted the temptation to explore other areas of Jewish history that were outside of his thesis (we can research Judah Benjamin on our own, e.g.). This is a great read and with the emphasis on interdisciplinarity and teaching entrepreneurship in schools, this would make an excellent addition to summer reading lists.