true Great Britain is an example of a core nation
During the early 1800's he attempted to organize a confederation of tribes to resist white settlement. During the war of 1812, Tecumseh and followers joined the British to fight against the United States. They fought against white settlement in 1812 and he was killed during the war.
There was no unified state that could grow all parts of life equally so they had to depend on trade in order to get goods that they needed from each other since they couldn't develop all parts of production or manufacture. Ones would for example have a developed pottery industry while the others would have mastered making Olive oil so they would trade in order to get what they needed because they couldn't make it on their own.