Would it be the mantle? It's the deepest layer and obviously the hottest.
Its spread mainly because of the pest rats and also fleas
I think because they are different types of breeds
The correct answer is - increased wealth.
Public safety, national defense and public services are all a must for every country's government so that the country can function normally. Increased wealth is not a must, even though every country's government would be more than happy to have it.