Historically speaking, it would be the "Erie" canal that has been the most important to the US, since this canal provided for the relatively fast transport of goods between states.
Answer:
The British (I think)
Explanation:
As they would have supported the South more but it would have been very difficult for the British to unite their people to a war if it would have supported slavery since there were labor issues arising in Britain at the time.
Answers
Because this day started
Answer: Recess appointment
As the name implies, these are appointments the President makes when the congress is in recess. This is when congress-members go back to their states and districts.