Twice now a minor settlement (Tenpines Bluff) has been attacked.

The first time, I got a message about it being destroyed, so I loaded an earlier savegame and went to defend it.

The second time, I think the Minutemen fought off the attack, because when I arrived to improve their defences, there was an armed squad of Minutemen standing around. They didn't stick around, so I assumed they were a mobile unit responding to distress calls of any settlement with a radio antenna (they have one).

Can anyone confirm if the Settlement part of the game is optional?

I can't go running around defending every Settlement there is, I'd be doing nothing else but fighting off Raider groups or whatever!

And I don't exactly have the resources to build a battery of automated guns at every Settlement I come across.

Its optional. I have left a settlement go unnoticed/undefended many times and somehow there are still 12 people there regardless of the 21% happiness rating.

Make sure you have enough defense and then you will not need to micromanage/defend smaller settlements. Always have a total defense number superior to the water and food total. In practical terms for a small settlement of say 2 or 3 settlers which produces 3 water and 6 food (9 total), build two tourets for a total of 10 defense, 3 for 15 if you want to make sure.

Small well defended settlements do not get attacked often, if at all. Larger ones which produce a lot of food and water (for instance my Castle settlement which has 24 food and 40 water for now) will get attacked more often from what I can tell, but the same principle applies = larger number of defense. I have 76 defense there (machine gun tourets and a few soldiers).

EDIT: In my game my small settlements have never been attacked but I built tourets as soon as I got them. The only attacks I had were on Sanctuary and the Castle, which produce massive amounts of food and water. Raiders and Mutants want to put their hands on the goodies.

I stopped bothering with them except for a couple settlements I built out. The rest I just scrapped everything there until the people left (or I handled it another way which I won't detail here to not break rules). It makes for an empty wasteland, but there's just too many settlements and they are much too needy. I feel like this feature could have been really awesome if there was one or two major settlements for us to build out - maybe four max to cover the four corners of the map. Having so many with some of them maybe supporting 2 people just doesn't seem like it was worth it.

Fewer settlements with more options in the building of infrastructure would have been better, in my opinion.

I am putting off any Settlement development until I have played the game. Well, I mean doing the quests and exploration. Then I might have time or inclination to tend to them.

Well you don't have to establish settlements at all really and I hear you can just tell them to go to an established town.

What I did notice is that if you try to establish settlements as fast as Preston hands out missions well your going to get overwhelmed with just how much stuff you have to build to defend them.

The problem with the Settlement attacks is apparently it can be triggered just by me going near them on the way to somewhere else!

Or by something else in the area.

Example:

I was on the way to a Virgil's laboratory and on the way, I passed this racing track full of robots.

I ran the gauntlet of enemies to the control terminal, shut down all the robots and then went to say hello to all the enemies with Strong accompanying me.

After clearing the racetrack of all opposition, I noticed there was a prisoner near the terminal.

I then rescued the prisoner and followed them home.

That home happened to be Nordhagen Beach, which happened to be a Settlement!

And then there was Greygarden.

I was going to Wastewater Treatment Plant to get Strong some supermutant armor and when I discovered there was a mission for it, why not do it at the same time?

Cue completion of the mission, another Settlement added!

So I doubt if you can avoid activating any Settlements at all, if this is the way the game works.

also you can consolidate settlers at other settlements so you can clear out and shut down smaller unused settlements to focus on the few larger ones.