Hierarchical tagging?

I want to use tags in my blog as categories, whereas some tags are “sub”-tags of others. So for example, “Amsterdam” and “The Hague” would be sub-tags of “The Netherlands”.

Why I don’t want to use categories is, becaause I want to be able to add “Amsterdam” also to the “higher” tag “Capitals” (Together with Paris, London), and “The Hague” to the top-tag “Government seats” (again with Paris and London)

For this, if I tag a post “Amsterdam”, it should be automaically be tagged “Capitals”, and if I tag a post “The Hague”, it should pop-up in “Government seats” and in “The Netherlands”.

I think that another possiblility would be to “tag” categories. Eg. that categories can be appointed several tags, so then the “Amsterdam”-category would be tagged “Capitals” and “The Netherlands”

If I can make this work, I want to hide my category list from my side-bar, and show the hierachical tag list instead.

Does this make sense? See the blog https://climatesceptics.org for where it should be applied.

Does anyone have a tip for a plugin I can use?