Got an issue over a certain move..
I had this argument with my friends many times before so i decided to go ask the experts..
Can i build a settlement in the middle of another player road streak if the result would be leaving the other player roads attached to no settlement or city?
And if i can, does it cancel his road streak?
I found a picture to demonstrate that situation
Sure can you build a settlement there and the other player can build the road to the next possible place for a settlement.
No Problem at all.
The settlement cancels the count for the longest road there
As already mentioned, you can build here and it does break their road (and that might also transfer the longest road to the next longest road, if 5 or longer), and they can keep building road on that unattached road.
This might be desirable though as even if they know you will build a settlement and break their road, building that extra road allows them to keep building after that point, if they are trying to get to a key resource or port (or simply not be trapped with no where to build)