Naturalizing provinces

For my short time playing this game i have come to realize that non-core-provinces are not very helpful resource wise. If their was a system to naturalize conquered lands from 10% resource production to 50 or 60% resource production maybe 10-20 days later, it would improve upon the need for reaching out and attacking other nations for resources. Core provinces would still be top in resource production by far and would not need any naturalization if reconquered.

Many wars are fought for resources like Japan's invasion of mainland Asia in World War Two and fighting for resources has been part of history since ancient times. In history as each empire conquered another, the civilians took a little bit to get used to their new ruler but once they did they produced resources better.