I would say its because no one really decided to change anything. No one during the old ages really knew how to do anything and only used what they had and what was closest to them.
I believe it was Douglas MacArthur because in 1951 MacArthur wanted to take all of North and South Korea but president Truman said no
The colony of Georgia was established to serve as a military protective zone between the English colonies and the Spanish settlement in Florida.