Enslaved workers supported the Southern economy because they harvested crops on the southern plantations, and this helped the South's agriculture-based economy.
The Mississippi is important to American because of how long it is. It starts in Minnesota and drains into the gulf of Mexico. Many people have built their homes along and near the "Mighty Mississippi" because you can transport goods down it via boat to many states, you can use it to farm and get water to dry locations and grow many crops. It's used for hydroelectric power for large cities, it drains off flood water to prevent flooding in the Midwest. It was very important during the civil war and many boats battled for control of it. And it's a lot cheaper and faster to transport on the river than on the road, it has many dams that help local economies and create job opportunities for locals.
