Marx and Engels really didn't get America, like at all. We're a country of schemers and backstabbers, and collectivism of the German sort was alien to how Americans saw themselves and their aspirations. If you want international solidarity, or labor to unite, it does not come easily. But then, the labor movement around the world was plagued with fighting within labor, between who was the more worthy workers and who could defend their interests. The vast unskilled workers could not do much for their position, and would be fought by their skilled counterparts. This became more established as the "labor aristocracy" emerged, as the "better of the poor" were sorted out - precisely in line with Whig/liberal thinking of the 19th century. Really, it took the laughable incompetence of the European and American ruling classes for labor to gain as much as it did, and as brutal as monopoly capitalists could be, they often lacked what it took to really grind down the populace. It took the invention of eugenics and fascism, and their emergence as the ruling ideologies, to really begin the process of reversing the trend towards a stronger middle class and labor's recognition of its own power (despite labor's internal conflicts); and this process really only began in earnest in the last third of the 20th century, because in the short term it was necessary to improve the lot of the commoners enough to build that technological base to make the national security state work.