Re: Historical events

Allison and Roger... see examples below.  Yes, you can still use Event.
When you don't have a startDate or endDate, then just leave them excluded.
The use of additionalType and referencing other ontologies or Wikidata is
quite useful and a generally accepted best practice when you need to easily
subtype things that Schema.org has only general types available.

{
  "@context": "http://schema.org",
  "@type": "Event",
  "sameAs": "https://www.wikidata.org/wiki/Q327052",
  "additionalType": "https://www.wikidata.org/wiki/Q15815670",
  "name": "Battle of Aachen",
  "startDate": "2 October 1944",
  "description": "major conflict during World War II",
  "endDate": "21 October 1944"
}

{
  "@context": "http://schema.org",
  "@type": "Event",
  "sameAs": "https://www.wikidata.org/wiki/Q11761",
  "additionalType": "https://www.wikidata.org/wiki/Q15401699",
  "name": "Bronze Age",
  "description": "prehistoric period",
  "about": "Historical Event"
}

Any other questions ?
-Thad