Some marxists believe that conflict between medieval burghers and small merchants on the one hand, and the nobility on the other, 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

This form of historical change is explained by the idea of Dialectal model. In Dialectal model, the idea keeps on passing to and fro among various groups before arriving at a particular decision. Hence in this case, the idea of modern capitalism was with the conflicting stakeholders and then it passed on to the nobles and finally the idea of modern capitalism was derived.