What you just described, this “mild nationalism?” There’s a word for that: patriotism. Nationalism is extreme patriotism

This is just false. Nationalism is just the idea that a nation should be sovereign. The Meriam Webster definition you cited is just a contemporary definition, the original definition is the second one listed here:

: support for and promotion of the political independence or self-determination of a nation or people

Source: https://www.merriam-webster.com/dictionary/nationalism

Nationalism isn't a more extreme version of patriotism. Nationalism describes an ideology while patriotism describes a particular set of emotions. The two could overlap, but they're not the same thing at different points of a spectrum.