Hitler's Germanic nation is the best nation. Does this Germanic nation refer to a single Germanic nation or to the whole Germanic nation?

What you said is almost the same. Germans have existed in Europe for a long time. They spread all over Europe and even around the world by changing their beliefs, tribal wars, immigration, intermarriage with foreigners or foreign wars. Hitler deliberately pointed out that the Germanic nation is the best nation in the world, mainly referring to most Germans, in order to win people's hearts.

Personally, I feel that every nation has advantages and disadvantages, and a nation without disadvantages will be hated by other nations and will go to extinction. When a nation only sees its own advantages and fails to see its own shortcomings, it becomes an arrogant nation and a dangerous nation, which will be rejected by other nations.