The complexity point is the seventh and final rubric point. It requires your essay to demonstrate a complex understanding of the historical development in the prompt. This is not a separate paragraph you add at the end. It must be woven into your argument through one of four recognized moves: explaining both similarity and difference, explaining both continuity and change, explaining multiple causes or effects, or explaining relevant connections across time periods, geographic areas, or themes.
Read your practice essay. Can you point to one specific sentence or passage that demonstrates complexity? Does it do more than mention a second topic? Does it explain how the complexity changes or deepens your argument?