Although I can't provide a full answer, I can offer my 50 cents on how Marx's methodology was distinctive.

Unlike the history preceding it, Marx's methodology was founded upon a sociological analysis. Although this was present before Marx and Engles' time, it wasn't the defining feature of academic work of the time. Furthermore, rather than looking at Great People such as Napoleon, Marx's methodology looks at groups identified by their social and material power. I.e. the workers and the factory owners. In doing so, Marx introduced a material history, whereby we examine resources as a way to understand the past.

When compared to the schools of thought preceding this, we see a big change. The Hegelian school of thought was based around the 'Spirit', the idea of moving forward and that the changes and transformations in social groups were influenced by the progress towards a "higher" level of humanity. In contrast, the analytic focus of Marx was on the idea of revolution and that the higher level could only be achieved once social antagonisms had been eradicated.