The 1850s and 1860s may be said to mark a philosophical boundary distinguishing the young Marx's Hegelian idealism and the more mature Marx's scientific ideology associated with structural Marxism. However, not all scholars accept this distinction. For Marx and Engels, their experience of the Revolutions of 1848 to 1849 were formative in the development of their theory of economics and historical progression. After the "failures" of 1848, the revolutionary impetus appeared spent and not to be renewed without an economic recession. Contention arose between Marx and his fellow communists, whom he denounced as "adventurists". Marx deemed it fanciful to propose that "will power" could be sufficient to create the revolutionary conditions when in reality the economic component was the necessary requisite. The recession in the United States' economy in 1852 gave Marx and Engels grounds for optimism for revolutionary activity, yet this economy was seen as too immature for a capitalist revolution. Open territories on America's western frontier dissipated the forces of social unrest. Moreover, any economic crisis arising in the United States would not lead to revolutionary contagion of the older economies of individual European nations, which were closed systems bounded by their national borders. When the so-called Panic of 1857 in the United States spread globally, it broke all economic theory models, and was the first truly global economic crisis.