In 1860, the institution of slavery was firmly entrenched in the United States; by 1865, it was dead. How did this happen? How did Union policy toward slavery change over the course of the Civil War? Why did it change?

Civil War

In 1860, the institution of slavery was firmly entrenched in the United States; by 1865, it was dead. How did this happen? How did Union policy toward slavery change over the course of the Civil War? Why did it change?