Explain how and why the United States constructed and maintained a system of racial slavery.

Examples of How: The US government had a law that only white and land owning men could vote in elections, preventing African Americans from voting.  The Fugitive Slave Act of 1850 allowed slaves who had escaped to the North that were "free" could be brought back to the South, including not only runaways but even African Americans who weren't associated in the South.

Examples of Why: The purchase and sale of slaves was (probably) a big economic factor within the US, causing those who owned them to be able to sell slaves for lots of money. Many farms and plantations in the South claimed that slaves were economically necessary to harvest and and process crops.