Distinguish between river and stream

Streams are shallower than rivers. Streams are more turbulent and aggressive than rivers. Streams erode stones, sculpt the surface of the earth and carry the sediment into rivers that carry all the sediment into oceans and lakes. Streams flow within narrow banks while rivers flow within wider banks.
Or

Streams are bodies of water that have a current; they are in constant motion. ... Rivers are the largest types of stream, moving large amounts of water from higher to lower elevations. The Amazon River, the world's river with the greatest flow, has a flow rate of nearly 220,000 cubic meters per second!

It is the doctrine that the us had the right and duty to expand throughout north america. it just means they believed they had the right to expand westward and they did! they stated with the 13 colonies and then they kept moving gaining different territories throughout the years