What is the central idea of nazi race theory?

In Nazi propaganda the "Mediterranean" race was described as brown-haired, brown-eyed, light skinned but slightly darker than their Northern European counterparts, and short …

"Hitler's Nazi theory also claimed that the Aryan race is a master race, superior to all other races, that a nation is the highest creation of a race, and great nations (literally large nations) were the creation of great races."

Explanation:

http://www.nazism.net/about/ideological_theory/

lincoln declared that slavery should not be allowed to spread into the new states, and of course this angered the south at the time.