C) Slaves
Slavery grew due to the rise in demand of cotton.
The US introduced industrial power and new weapons. To protect their country from being taken over by the US or another foreign power, Japan decided to become a "western" power. The US opening Japan to trade exposed them to the methods of a modern country.
Each branch of government controls a certain aspect of the other.
Legislative can restrict the policies of the executive and judicial.
Judicial can strike down legislation deemed unconstitutional, and undo executive decisions through rulings on their constitutionality.
Executive Orders can bypass legislative channels for more efficient decision making, and can nominate if not alter the Supreme Court along with taking part in it's processes. ( Some of this is my own interpretation. )
The idea for the removal of Native Americans was first brought up by Thomas Jefferson, who wanted the natives to willingly leave the colonies. The act gave Jackson the authority to offer the native nation's land west of the Mississippi in exchange for their eastern lands. It also provided money for the law to be carried out. When some tribes refused to sign the treaties, they used physical force to remove them, hence the Trail of Tears.
