Your research term paper will be a consolidation and expansion of your three short essays. You must pick one of these three essays to develop into the backbone of your paper. The other two essays should then be revised and expanded so as to support and elaborate upon the thesis of your back-bone essay. 

For example, let's say that you want to base your entire term paper on Essay #1. The thesis of that paper thus becomes the backbone of your work in progress. Essays 2 and 3 correspondingly become the extensions of your definition of a given period or movement. With this in mind, you might decide to elaborate on your definition by pointing out how various artists of the period/movement (including the two you examined in Essay #2 AND perhaps one or two more besides) embody and elaborate upon certain elements of its definition. And you may also want to consider how various influences that acted on the style of the artist you considered in Essay #3 also served to influence other artists in that period. Those influences that seem to be more widespread may possibly become part of the way you define the period/movement in general.

You will find that much (but not quite all) of the actual writing of this paper is already done. The challenge here is to incorporate big chunks of your earlier work into a single, longer essay. To do this, you will need to conduct some more research so that you can balance out your paper (giving proportional consideration to each artist that you bring up in your discussion). You'll also need to write some transitional passages that smoothly connect the recycled parts of your discussion together into one coherent presentation in which you support and elaborate upon a single, clearly articulated thesis. All digressions must ultimately be drafted into the service of this thesis. If they are not, then they should be omitted from the paper.

If your paper runs short of the minimum length-requirement (2,000 words, or roughly 8 pages) then you might consider discussing another artist or perhaps some more specific works of art by each of the artists you bring up. But these last-minute additions should not function as mere padding. Try to use them to shed additional light on a particular aspect of your thesis that may have been neglected in the shorter version of your paper.