Also how does one gain an A? As in, is it the links which are most important, argument or a combination?
You need to have a look at this page from the O.C.R. website. It includes all the documents which might help you, including mark schemes.
From these it is clear that the top-scoring essays are those which do the following:
Show good subject knowledge by using accurate and detailed evidence;
Are clearly structured;
Show an understanding of the relevant historical issues and their context;
Are consistently analytical with developed explanations;
Evaluate a range of relevant factors, AND;
Come to a supported judgement on their rleative importance and/or links.
I hope that helps. You don't have to all these perfectly, but it's what you are aiming for.