Welp they both had two great oceans between them, a land invasion is near Impossible, and a sea attack would not be smart for the Central Powers/Axis
An Air attack needs refueling and no enemy had a close airbase plus we had anti air any attack on North America or any of the Americas is useless.
Mantle are made up of molten rocks. Which is known as magma.
The main difference between the thickness and density of earths crust and mantle is the material making up each section. temperature and function also differ between the two sections
