when structuring your essay it is at first Key to what I call, "figure the riddle" in the question, this is perhaps more important at A-level than it is at GCSE but it is important none the less. And by this I mean finding out what the question actually wants you to do because so often students write a great answer but do not answer the question. For example in a question such as "explain why rivalry developed between Britain and Germany in the years 1900-1914." It is very easy to write a very long essay on what the rivalry caused and what was the result of the rivalry but you would receive limited marks as the question has asked you why the rivalry was created and not what was a cause of the rivalry- this seems a really simple task but has proved costly for many students.
when actually writing your essay I would stick completely to PEE- P-point- what is your argument, make sure you can develop this argument.
E- Example- you always need to use an example to prove that your argument is valid, it doesn't matter what your point is, if you can prove it with an example then it will be valid and mark worthy m.
E- Evaulation- this is perhaps the most important at A-Level but score you high marks at GCSE too. This is the hardest of the three tasks as it means you have to show why your argument is important. So you have given a point- given an example- now it is crucial to say why that is important and it is here in your answer that you complete the question.
that is the structure I would use for my History essays.