Einheit zur Freiheit means "for unity and freedom" and was the motto for the unification of the German states into a federation in the 1800s. Zur Erinnerung means "for rememberance" ... of the franco-german war of 1870-1871. Most likely it is just a commemorative made by German immigrants or German-Americans in the late 1800s in St. Louis, which had a lot of German influx during that time (think: Anheuser-Busch) , but also had a strong French heritage as a French settlement in the Lousiana purchase. So naturally there would be more local interest in St. Louis of the Franco-Prussian war than in most other cities, along with possibly Cincinnati which was also heavily German but lacked the unique French aspect of St Louis.
From wiki:
"Steamboats first arrived in St. Louis in 1818, improving connections with New Orleans and eastern markets. Missouri became a state in 1821, at which point the capital moved from St. Louis. However, St. Louis was incorporated as a city in 1822, and continued to see growth due to its port connections.
Immigrants from Ireland and Germany arrived in St. Louis in significant numbers starting in the 1840s, and the population of St. Louis grew from less than 20,000 in 1840, to 77,860 in 1850, to more than 160,000 by 1860."VERY COOL MEDAL!!
