A new book by a scholar of the American right-wing examines the Alt-Right. This is the best and most comprehensive work on the Alt-Right that has been published to date. Available from Amazon. A number of reviews are currently available from mainstream as well as libertarian, far right and far left sources. See here, here, here, here,here, here, here, and here. I recently discussed the Alt-Right myself at a talk given to the H.L. Mencken Club a couple of months ago.
I generally think the future of the United States will be somewhere in between the super optimistic predictions of Joel Kotkin and the super pessimistic predictions of Ellison Lodge in his review of Kotkin. The United States will continue to recede as a global hegemon (a good thing), but will continue to be an economically and technologically highly advanced state. The general society will become increasingly more integrated along racial, ethic, cultural, religious, gender and sexual lines at every level, from top to bottom. However, class divisions will continue to widen and increasingly resemble those found in Latin America. A super diverse society with huge disparities of wealth will certainly generate plenty of social and political conflict. The role of the state will be to manage such conflict by playing off different groups against each other, buying the loyalty of some groups, suppressing others, negotiating settlements between others, and forcing settlements in some instances. Many paleoconservative types have long predicted that the USA will look increasingly like Brazil in the future, and I suspect they are correct in the sense that the USA will be a major economic power that is highly diverse culturally, but with a very high level of class stratification and social conflict.