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
Answer:
Westward expansion meant that the US acquired ever increasing amounts of land, and needed people, farmers, to settle there so it could maintained without a huge military presence. This led to massive immigration in the second half of the 19th century, as mostly Europeans came here seeking to finally have their own land.
It also added vast resources to the United States, both in terms of potential agricultural production and things like gold, silver and timber.
It stimulated the construction of the Transcontinental Railroad, and added new states to the country.
It further aggravated the divide between north and south, and accelerated the onset of the Civil War.
Explanation:
B) European countries and the United states
