According to British social theorist , societies developed through a process of "struggle" (for existence) and "fitness" (for survival), which he referred to as the "survival of the fittest."

Herbert Spencer

Explanation:

Herbert Spencer was an English Biologist, Philosopher and Sociologist. He used Darwin’s law of evolution and was known for his dogma of Social Darwinism. He proposed that a society will evolve over time as in the case of living organisms.

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.