For Spain, such an issue is inevitable. Originally, the population gap between these two cities and other small and medium-sized cities was already large. With Carlo becoming the King of Spain for the past decade or two, the development rate of these two cities has left others in the dust, ultimately leading to the twin star cities having an ever-increasing population, while other cities' population growth rates evidently cannot keep up with Madrid and Barcelona.
In the short term, the larger the population of the twin star cities, the more beneficial it is for Spain. The Barcelona Industrial Base offers hundreds of thousands of jobs, yet Barcelona only has 880,000 residents, which is clearly quite unreasonable.
