Originally posted by HAHAHuH?:

Quick answer is yes you do get events that progressively escalate with each boss you've defeated. And it is strongly recommended to dig trenches and put up walls and fortifications as certain areas you have to build will be progressively more hostile.

Uhm no, sorry, but no.
It isn't your home that is attacked... it is you.
The raid events may centre on your base (the red circle in the mini-map denotes the raid event area), however the raid is directed at you.
If you are not present or unreachable, the mobs may attack structures, but if you are open to attack and reachable, then every mob involved in the raid will target you.
@OP For this reason, no, it is not necessary to build any fortifications, trenches or walls.
All you have to do in the event of a raid, if you fear for your base structures, is to draw the mobs out and away from them so that they may target you and you alone. This is easy enough to accomplish and whether you opt for melee or ranged attack in order to wipe it out is up to you and your combat competence.
https://steamcommunity.com/sharedfiles/filedetails/?id=2424562622