America's extremes are tearing it apart

One of the regular topics of discussion in the media in the US recently has been how polarised and divided the country has become, even to the extent where there is regularly speculation about what a new civil war would actually look like, if things continued to worsen. How did America get here? How did it end up with two parties of extremes circling a hollowed-out centre? How did it end up with weakened political institutions, and politicised non-political institutions? And what, if anything, can be done about it?