I always followed a very simple structure which appeared to work very well; the introduction would include two opposing historical views (quotes from historians to support them are great but not essential), where my view lies and how it corresponds to the two views presented and a bried explanantion of why this is my view. I would then write about four paragraphs, each covering one factor relevant to the question; the paragraphs would consist of a brief explanation of the factor, how it related to the qeustion and then how it relates to the historical views presented and how it supports my view (for example if the question was regarding the downfall of margaret thatcher, one factor could be economic conditions and the brief explanation would provide a brief summary of what the economic problems at the time were, how they led to her downfall, how this links to historians views regarding the downfall of Thatcher and how it suupports or links to my conclusion).