Answer:
Population growth in the eastern states.
Availability of cheap, fertile land.
Economic opportunity, e.g., gold (California Gold Rush), logging, farming, freedom (for runaway slaves)
new life
more food
Explanation:
A theory is a conclusion that is drawn from observations and experiments, but a law provides an explanation. this is the answer strictly because within science everything can be proven wrong nothing is set in stone
they both provide a good grip on the ground so you don't slip