Why did americans “dream” of linking the atlantic and pacific oceans by rail, as the author states?

Linking the Atlantic and Pacific oceans is called a transcontinental railway. This is a means to make trade and commerce easier and faster. These railroads will open a lot of opportunities for the western world to explore the rich countries of the east. It will open unpopulated regions and allow for the west to create networks within the Asian and Atlantic continents.

becasue in the south they disallowed slavery but in the north slavery was illegial this boilled into because mexico wanted slavery

china unilaterally claims the entire south china sea as sovereign territory, then builds artificial islands to bolster its claim. it suddenly activates an air defense identification zone over the east china sea, and threatens to down any aircraft that does not report its position. it builds roads into indian territory, then redraws the maps to show that it is actually chinese territory. the people's republic under president xi jinping is quickly becoming the bully of asia.