[kbs666]

you want tags for this.

Create tag sets for the continents, regions and countries that exist in your world. Then add tag snippets for those tags to each topic (you can make this the default for the incident category and time period category by editing the category definition). You should obviously make these tag snippets allow multiple tags to be selected.

For the description incident and time period already have description sections. Simply write your description of the historical event in their and the linking will occur as usual.

When it comes time to filter simply filter on the correct tag and you should get a list of the incidents and time periods relevant to that particular place.