Some Marxists believe that conflict between small merchants and the nobility led to the creation of modern capitalism, which was distinct from either of the opposing forces. What would Marx call this model of historical change

   A dialectical model

Explanation:  Essentially a dialectical model of change emerges during the interaction of opposing forces. It works something like this: to something that already exists, there is an antithesis that is the counterweight to the existing one, in order to create a new synthesis from the conflict that has arisen, which is different from both. It works in the same way as social and historical changes, in some existing historical system in this case feudal, noble, a new system of small traders, bankers, artisans emerges as a counterweight to the nobility. Then there is the conflict from which capitalism emerges, later modern capitalism, which is different from both these conflicting forces.

Marx also defined historical changes that occur according to a dialectical pattern, where contradictions, i.e conflicts that occurred in one period or at one level of development, are overcome at one of the next levels when a new system grows, that is, a historical change occurs. These differences of conflicting forces or systems, in this case nobility and small merchants, are incorporated into a new system, a new form of social order, in this case of modern capitalism.

corrupt also means cruel

where is the