The arms of the galaxy are in turn moving around as well. Its like a beautifully orchestrated ballet.
HS, I know you do not like the negatives, but the arms of the galaxies are almost stationary, standing waves. it is the material that is orbiting the center, and moving through them.
Fits your analogy though, certain features of history remain, different entities, empires move through the same stages, pressures, creations, etc. interesting.