(A) ** Access to new markets and resources
(B) Slave trade
(C) ** Closing of the frontier after America had expanded from coast to coast
(D) Protection against Chinese and Japanese invasion
EXPLANATIONS BELOW
Concept note-1: -Gold rush and mining opportunities (silver in Nevada) The opportunity to work in the cattle industry; to be a “cowboy” Faster travel to the West by railroad; availability of supplies due to the railroad. The opportunity to own land cheaply under the Homestead Act.
Concept note-2: -The three reasons the US expanded overseas was for economical power in overseas markets, to civilized non white nations like the Europeans did during the birth of America, and because the frontier was closed and Americans wanted to expand their influence.
Concept note-3: -Manifest Destiny, a phrase coined in 1845, is the idea that the United States is destined-by God, its advocates believed-to expand its dominion and spread democracy and capitalism across the entire North American continent.