Why is North America so developed?

North America has the blessing of both massive tracts of tillable land and the energy and natural resources to be relatively independent. These factors allow the continent to export the excess production to the rest of the world. There has not been a major war fought on the continent since 1865

first, the romans stayed isolated because they had to defend their own territories from neighboring cities that were harassing them, like the etruscans. second, once the romans managed to defeat their neighbors, and started to expand their territory, they started to build roads and bridges. finally, now that the romans have covered their territory with roads functioning as highways, they could mobilize their legions faster to assemble larger military units in a specific place

i’m   sure probably just geuss and see which one you can get right, i’m pretty sure it is the combination of goods and services