Business Schools across the country especially the IIMs promotes the academic diversity so that students from different academic backgrounds can bring fresh and unique perspective on the table during the discussion in the classroom. Students from different academic background such as Engineering, Commerce, Arts, Management, etc. get admission in IIMs. As you are pursuing History Hons and if get admission to IIM Ahmedabad, you will have to study different management related subjects which you have not studied during your graduation. The difficulty level of the journey will depend that how well you will be able to understand the course curriculum.