Don't see the point

What is the point of this game?

So far I'm new and I see all these different alliances but what is the need for them? To protect each other? Because all these alliances say "don't build in our SH" but my castle was planted right in the middle anyway! So what am I meant to do?

Are there rivalries between these alliances or are they just here for the sake of it? Am I allowed to take other people's castles or am I only meant to take the free ones?

So far all I see in this game is that we take free castles until there are none left... And if that's the case then there doesn't seem much point playing because it's boring...

There are most definitely rivalries between the alliances. The point is to be the most powerful essentially. Alliances will normally be peaceful at the beginning of the server while they set up but eventually someone attacks another person and it sparks wars an power shifts among alliances. You can take other players castles but it's much harder than taking a free castle.

Mostly...
Just hanging out and enjoying some good conversation. Get in a good active alliance.