I don't think one can necessarily US mix of divese racial and ethnic mix held back the US in terms of democracy. Quite the contrary. The US was the first country that began a serious democratization process. In 1800 the US as a whole was signifantly ahead of Europe as whole, despite the greater homogenity of individual European nations.
New Zealand, another diverse country which has quite a proud democratic history I think.
I do agree that racial diversity and legacy of slavery has created tensions in the US which made it harder to create a sense of unity in the US.
On the other hand Europe had challenges the US did not face in introducing democracy in that aristocracy and royality had a strong powerbase. Nordic countries did in fact have very strong monarchs. When Norway began the path towards democracy it was a challenge with how public officials and the military had long been showing alligiance to the monarch and not to any democratic institutions.
Ironically that seems to have also been an advantage. I have been reading a bit in Gunnar Myrdhal's An American Dilemma which is a Swedish analysis of American society in 1930s and 1940s. One of the things Myrdals remarks on is the poor quality of American bureacracy and government officials.
In the Nordic countries the bureacracies did not arise within a democratic tradition but within a merit based system under absolute monarchy, where credentials and performance mattered most.
In the US a lot more government officials got elected and thus a popularity contest rather than skill or merit would dominate in selection. E.g. as far as I know judges can still be elected in the US today without actual relevant education.
One of the speculations has been that one of the reasons Americans are so skeptical of government is because the government has been of low quality. I am not talking about the political leaders. The US seems to have had many good politicians. I am talking about public officials and bureacrats in the government who make sure decisions by politicians get carried out.
Sweden, is here a bit of an outlier, as they have a very poweful, competent and independent bureacracy. During COIVD19 you may have noticed how Swedish politicans were hardly noticable while their experts in the bureacracy ran the whole show.
Thus citizens in Nordic countries have probably developed a higher trust in government, because government has a longer history of competent decision making. One of the topics I did not cover which I should write about at some point is the Nordic belief in objective decision making. One of the founding principles in Norway was based on a belief in using statistics and data to make decision. The Norwegian statistical bureau SSB had a strong position from early on.
American democracy has perhaps been based more on strong ideas while Nordic has been more centered around pragmatism. This is more of a hypothesis. I am still trying to study this more. It is just a perception I am left with from what I read. I have no idea how one would quantify something like that.
