From a post I made last night:
A white supremacist believes the white race is superior in every way to all other races.
A white nationalist also believes the same thing, with the added belief that all races would be happier living separately. White nations, black nations, brown nations, etc. To support their argument, they point to the Jewish nation (Israel).
A couple decades ago, the KKK and Nazi ranks were so depleted, they decided to join forces and call themselves White Nationalists.
Among white nationalists, there are those who believe all the "mud people" should be invited to leave the United States and be financially compensated for their property, and then all the colors of nations will live happily ever after.
Well, sort of. Being white supremacists, WNs believe the other color nations will eventually die off from being so darned inferior. With the possible exception of the yellow nations.
Other WNs believe the mud people should be made to leave the white nations at the point of a gun without financial compensation.
Still others can't wait for RaHoWa (Racial Holy War) so they can commit mass genocide of all non-whites.
There are a large number of WNs who believe the white race is doomed to extinction, and they are pretty depressed and angry about it.
The Alt-Right is just a name some White Nationalists gave themselves to distinguish them from other WNs.
The WNs, Nazis, and Alt-Right are so far to the right that they call your average non-racist conservative a "cultural marxist".