What mistake did french commander general montcalm make in on the plains of Abraham?

French Commander General Montcalm made the critical mistake of engaging British forces on the Plains of Abraham without fully leveraging the advantages of his defensive position. He underestimated the effectiveness of the British troops and their artillery, leading to a poorly coordinated attack. Additionally, Montcalm's decision to fight in an open field rather than in a fortified position contributed to the decisive defeat of the French, ultimately leading to British control of Quebec.