Hi Audrey,
At this time, only Subject, Place, and Genre taxonomy terms can be linked to descriptions as access points, in addition to linking authority records as Name access points.
Taxonomies in AtoM are not just used for access points - any time you find a drop-down menu in AtoM's edit forms, it is usually linked to a taxonomy that contains the controlled vocabulary terms appearing in the drop-down. Many of these are customizable, though a few are locked, as they relate directly to either controlled terms take from a standard and used in a template, or else internal functionality (like the publication status, where the terms "Draft" and "Published" are in a hidden taxonomy).
Regarding this particular taxonomy - I'm pretty sure it's a legacy of an early beta version of AtoM that was never fully implemented. I can find evidence of it in ICA-AtoM 1.3 for example (
here), but at no time can I find evidence of it including default terms, or being linked to any entity in AtoM. To be honest, it probably should have been removed some time ago, since there is currently no way to make use of it as a taxonomy that I know of!
If you have local developers (or are one), then you could study the way that existing access points are implemented in the description templates and customize AtoM to add your own Historical events access point functionality.