The Germans from Russia emigrating to the Dakotas is well documented in history.  You are correct that the majority of Germans who came to the USA came directly from Germany.  Many settled in Missouri.  That is NOT however the case in North Dakota.  The Germans from Russia came a a later date than those who came directly from Germany.  In fact the Germans from Russia moved from Germany to Russia about the same time the earlier Germans moved to the USA.  A couple generations later those Germans who had move to Russia left Russia because they were being persicuted there and many moved to the Dakotas.