At its founding , it was the only fully professional soccer league in the United States .
The St. Louis Soccer League was based in St. Louis , Missouri and existed from 1907 to 1938 .
At St. Louis Soccer League 's founding , St. Louis Soccer League was the only fully St. Louis Soccer League   league in the United States .
The St. Louis Soccer League was based in St. Louis , Missouri and existed from 1907 to 1938 .