What the hell is manifest destiny?!?!?!?!?

there is this painting of this flying woman, ppl, baffalo, and indians. i hafto choose 6 characters (including) animals and write speech bubbles for them using all the words: destroy, manifest destiny, progress, growth, native ppl, transportation, communication, trade, and united states. i didnt pay attention in soc st class today and have no clue how those words relate. pleese help me understand what it is and how to use those words to describe the charcters thoughts and feelings!