It is the same with any kinda barbarian group. If your land doesn't give you resources, you learn to fight to take them from your neighbor. Your neighbor learns to fight to fight you. At some point the fighting gets too hard to be worth it so you go find softer targets. I saw a cool chart of Mongol migrations that show just this dynamic. The toughest army taking thr good land and the others being sent into he world to raid softer targets. Half the dynasties of China were started in that way if I recall. Fighting being a widely applicable skill let's you take over places and then you declare yourself kings and pretend you aren't just fancy warlords.

England is one of the few sources of tin that was known about in antiquity. So they were important for bronze. So thr only natural reauouces they had were ship parts and weapon parts. Which explains a whole lot on it own really.