I'm assuming by "Low Germans" you mean speakers of Plattdeutsch.

The Platt-speaking regions of Germany were part of the Holy Roman Empire, and most of them were later part of the Prussian Empire.

Educated Platt speakers used Hochdeutsch (Standard German) as a written and spoken language by the end of the sixteenth century.

Although Platt has a distinctly different medieval root from other Germans, it's considered by most German speakers to be a dialect on par with Saxon, Swabian, or Swiss (among others).

"Low German" doesn't indicate inferiority, or a separate race. It indicates literal elevation: Low German (Plattdeutsch) was the German spoken by the Germans living in the lowlands.

You will notice in the maps provided by /u/bocadelperro that Platt was spoken primarily in northern Germany. If you look at this elevation map of Germany, you will see that the land of Germany slopes gradually down from the mountains in the south into the North and Baltic Seas (the Baltic Sea is the Ostsee in German, meaning East Sea) in the north.

So it is not really a designation of status or inferiority (unless you want to get into southerners feeling superior to northerners, and all the various fun regional attitudes towards each other), but simply of elevation.