Assess the role of each of the following in causing the First World War (1914–1918): the desire for revenge; economic motives; Balkan nationalism.
Questions using, 'assess' are not looking for a one sided argument, they are implying that there is more than one answer and asking you to evaluate which you would consider more important.
With questions which introduce directly three causes you can approach it in a number of ways, by evaluating them seperatly in differnt paragraphs, although this technique may lead to a formulaic and un-integrated argument without follow of comparison. Chosing one you think most pertinent, and then using the following paragraphs to compare in order to assert why the other causes aren't as important. Or you could even take a flowing approach seeing it as a narrative, and assessing them individually but lonking each by giving the causes a chronologial order of impact.
Regardless of how yuo chose to structure your introduction, you must be able to concisely present this in your introduction. Using markers such as, 'firstly, next, moreover, therefore, secondly, and finally in order to sign post your arguments course. Remember to answer the question breifly in the introduction, although this seems strange it proves to the examiner that you have considered the point and know how your argument will develop.
Initially, make a mind-map, bullet points, or just a couple of sentences that detail what your argument is, and which of the three causes you consider to be the most significant factor. You can also argue that the factors are important in different ways, your assessment can therefore take the course of an exploration of each cause.
For example, Economic factors can be closely linked to empire and the disputes these casued as nations tried to build the most profitable and expansive empires at the expence of each other. This can be identified as background issue that introduced tension and conflict within Europe.
Whereas Balkan nationalism is a more immediate and contentious cause, inspired partly by imperial empire, the BAlkans question casued unrest and disquiet in the region, which nearly came to ahead multiple times across the ecade before the erupted.
It was the nationalistic inclinations of many that led to the terror attack in the form of the assassination of Arch-Duke Frans Ferdinand. Revenge in the context of this incident was used as an explantion for the agressive actions of the Austro-Hungarian Empire against the Balkan nationalists in Serbia. Therefore, revenge is ultimately the trigger but it cannot be seperated from economics and nationalism, the driving factors which led and escalated the revenge sought following the assasination.
This is only one interpretation, and as long as you are able to justify your argument you should folllow whatever cause you think is best. As long as you always remeber to justify it!
Although not essential, introducing historiography into your essay is a really clever way of showing the examiner that you have read around the topic and that you have formed your opinion based of investigation of the topic. You don't have to chose a historian that agrees with your point, you can use one which counters you rargument to show engagement with other ideas, but be sure to explain why you don't agree with their argument and why your is a more reasonable explanation. Remember be critical of the historiography, such as whether its a contempory spurce and implications thereof.
Conclude by summerise your argument, and reiterate your assessment of the causes.