Among the powerful nations, the existence of the United States is definitely the most unique and the most complex in terms of its comprehensive national conditions.
As an immigrant country, especially as the most popular destination for immigrants before World War I, the United States has a diverse array of ethnicities.
Although collectively referred to as American people, there are distinctions among British descendants, French descendants, German descendants, and so on.
Furthermore, the previous slave trade, along with immigrants and stowaways from East Asia, resulted in a population in the United States that comprised Black, Caucasian, and Asian races.
More crucially, the famous Lincoln granted civil rights to Black people, and although this helped the United States win the Civil War, the conflict between Black and Caucasian people became a significant factor affecting the stability of the country.