A-Level History non-source based exam questions almost always focus on the significance of one event/factor in relation to others. In this way, your essay should always seek to reinforce the significance of your leading event/factor.
It is important to begin with an introduction and end with a conclusion. A-Level History requires you to present a sustained argument, therefore, opening and rounding off what you are saying is crucial. Your introduction should look to lay out the significance of each event/factor then make clear which one is the most significant. I would always advise presenting a judgement in the introduction. Your conclusion should largely adhere to the same criteria with you running through each factor's significance then giving a final judgement as to what the leading event/factor is and why.
The main body should concentrate on affirming the argument you set out in the introduction. Supporting each factor with relevant factual knowledge is key. Select material based on what adds value to your argument. You should look to undermine all factors/events (excluding your leading one) before moving on to discuss something new. Reinforce your leading factor/event by asserting its strengths in comparison to your other factors/events.