What did people mean by slavery being a "necessary evil"

legislative branch:

one of the three branches of government divided between the senate and the house of representatives.

- creates or makes laws

- power to override a veto

executive branch:

one of the three branches of government, headed by the president.

- enforces or carries out laws

- power to veto a bill sent to it by congress

judicial branch:

one of the three branches of government, headed by the chief justice of the supreme court.

- interprets laws

- power to declare laws or actions by the government unconstitutional