what do Marx and Engels explain the triumph of bourgeoisie over the feudal aristocracy?

gradesaver has already addressed this at length in its summary of the Communist Manefesto. I am providing an excerpt below, and also providing the link to the entire article.

"It was the bourgeoisie‹"modern Capitalists, owners of the means of social production and the employers of wage labor" (79)‹who were the agents of these economic revolutions.

The new economic powers of the bourgeoisie led to their political empowerment. While the bourgeoisie had originally served the nobility or the monarchy, they had come in the middle of the 19th century to control the representative states of Europe. In fact, as Marx famously notes, "the executive of the modern State is but a committee for managing the common affairs of the whole bourgeoisie" (82). With this political empowerment came the destruction of the social fictions on which previous societies were based. Instead of focusing on the relationship of men to 'natural' superiors and inferiors, both in this life and the next, or even the indistinct Rights of Man championed in the first half of the 19th century, the bourgeoisie introduced an ethic based on the absolute right to free trade and the rational, egoistic pursuit of profit.

It was not enough, though, for the bourgeoisie to radically change all that has preceded it; it must constantly change in the present in order to expand and exploit its markets. As Marx says, "Constant revolutionizing of production, uninterrupted disturbance of all social conditions, everlasting uncertainty and agitation distinguish the bourgeois epoch from all earlier ones" (83). This economic and social dynamism unsettles the boundaries of nations and creates pressure toward globalization, amounting to an economic imperialism which demands that other nations assimilate to bourgeois practice or be cosigned to the economic backwater. In this way, the bourgeoisie "create the world after their own image" (84).

Marx uses the above story of the bourgeoisie's evolution to substantiate his central contention that the forces of production develop faster than the sociopolitical order in which those forces of production arise. The result of this disparity is a radical alteration of the sociopolitical order that allows it to catch up with the forces of production. Marx claims that this is what occurred in the shift from feudalism to bourgeois capitalism. This process, though, has not stopped. The conditions for the existence of the bourgeois order are being undermined by the new forces of production which the bourgeoisie themselves have ushered in. This is evidenced by the many economic crises‹results of an epidemic of overproduction, which Marx sees as a consequence of bourgeois economic development‹that rocked Europe in the 1830's and 40's. In response to these crises, the bourgeoisie either scale back their production, find new markets, or more thoroughly exploit old ones. According to Marx, though, all this is for naught as it does not treat the underlying problems which will create more acute crises in the future. Indeed, the underlying problems cannot be suitably treated as capitalism contains within it the seeds of its own demise, seeds which it itself nurtures through the necessary creation and ultimate exploitation of a new class, the proletariat........"

For more information;

http://www.gradesaver.com/communist-manifesto/study-guide/section1/