Positive: U.S gained more territory, more land means more power, more land to farm and greater profits from growing or making goods. The impact on the land wasn't so good though, the U.S used dynamite to blow up mountains and destroyed a lot of the country by building or taking from the land, it was needed of course but it impacted the environment.
Negative: hurt the land and the native Americans, the native Americans were forced off of their land and they had to find new places to go. Also, colonists brought over diseases and sickness that hurt the native Americans.
The painting above shows colonists chasing and killing animals, stealing the native Americans food, running Indians off their land, and us plowing land for our use, also us building railroads and creating a big mess. I think the angel represents the lives lost over the manifest.
I hope this was the assignment I thought it was and I hope I got this right! :)