The thirteen original British colonies in North America(, some formed as commercial ventures, others as religious havens, )each had a written charter that set forth its form of government and the rights of the colonists.
把括号部分去掉就是句子的主干 这里each是副词修饰had
相当于“ The students are both good. / They all finished the race." 中both、all的作用
The thirteen original British colonies in North America, some formed as commercial ventures, others as religious havens, each had a written charter that set forth its form of government and the rights of the colonists.