Complex sentence: Minor immigrations had also followed until Russo-Turkish War, 1877--1878 when the major wave of immigration involved immigrants from historic Georgian regions that had considerable Muslim populations like Artvin, Adjara, Ardahan, Samtskhe, and Guria.
Split into simpler sentences: Minor immigrations had also followed until Russo-Turkish War, 1877--1878. The major wave of immigration involved immigrants from historic Georgian regions that had considerable Muslim populations like Artvin, Adjara, Ardahan, Samtskhe, and Guria.