Prior to WW1, Germans were a large minority in Imperial Russia, they were represented in large numbers in the merchant/intellectual classes, and Germans, particularly Mennonites were encouraged to settle and build communities in many areas in the Ukraine. I believe I recall reading there were over 2 million.
The German army occupation of the Ukraine in 1918 protected the communities against the anarchy and pillaging that was going on in the rest of Russia because of the communist revolution. Before withdrawing from the Ukraine, the German army provided leadership, training and arms to form local self-protection or "selbstschutz" units who for a time successfully defended the communities against the anarchists. Some of these units fought together as part of the White army in the Russian Civil War.
"Selbstschutz group from the villages of Blumenort, Tiege, and Ohrloff, 1918":