How should I deal with counterarguments in an essay?

You should clearly set out your position in an introduction. Before you even start writing, however, you should go through a planning stage, in which you produce different explanations based on the evidence and set them against each other. Yours should be whichever emerges strongest from this process. Your essay should essentially repeat this - bring up counterarguments when you feel they are relevant, but always try to account for them and hold to your own view.