California became part of the united states in 1848. soon after, thousands of people migrated across the country to settle in california. this mass migration took place because

Soon after California became part of the United States Gold was found in the region of California and resulted in the mass migration of the people to this region. This period was also called Gold Rush because of the rush Gold attracted to this region. It was estimated that around 300,000 people migrated in the hope of good fortune.

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.