Final answer:
The two predominant ethnic immigrant groups that changed the US population after the financial panic of the late 1830s were the Irish, spurred by the Great Famine, and Germans, due to the aftermath of the failed 1848 revolutions.
Step-by-step explanation:
Following the worldwide financial panic of the late 1830s, the two most prevalent ethnic immigrant groups that changed the population of the US were the Irish and the Germans. The Irish immigration was largely a result of the Great Famine of the 1840s, while German immigration surged after the failed revolutions of 1848. In the late 19th century, these ethnic groups were followed by immigrants from Southern and Eastern Europe, including Italians, Jews, and Slavs, as the demographic composition of the United States continued to evolve. The Irish and German immigrants, despite their different reasons for migrating to America, shaped the cultural and demographic landscape of the country by establishing communities and becoming involved in American society. While Germans were largely accepted despite some initial cultural conflicts, the mostly Catholic Irish faced significant prejudice, particularly from the predominantly Protestant American society. Over time, discrimination against these groups decreased, partly because newer immigrant groups from Southern and Eastern Europe became targets for prejudice and xenophobia.