Subdivide

[Sarah]

To divide the parts of (anything) into more parts; to part intosmaller divisions; to divide again, as what has already been divided.The progenies of Cham and Japhet swarmed into colonies, and thosecolonies were subdivided into many others. Dryden.

[Dave Paprocki]

Divide (something that has already been divided or that is a separate unit)