By the outbreak of the war, St. Louis – the Gateway to the West – was a thriving and diverse, yet divided border town. Unlike many cities in the slave states, St. Louis was home to a growing community of European immigrants. By 1860, over half of the city was foreign born, most from the German Confederation or Ireland. The Germans were, by far, the most populous and influential ethic group in St. Louis. With 50,000 in St. Louis alone and united over the divisive issues of slavery and secession, they made a tremendous impact on the Union war effort in the city and their new home state. Just second to the Germans were the Irish, who accounted for nearly 30,000 (or 20%) of the city’s 161,000 residents. Missouri’s Irish – totally over 43,000 – was the highest population of Irishmen in any state in the South. Typically overlooked compared to the Germans, the Irish were more-so divided over the tense issues encapsulating their community. Their impact on the Civil War in St. Louis deserves more attention and further study.