Why were europeans forced to look for new resources ?

Slavery:

Time before the war, The South depended on slavery for labor to work the fields. Slaves could be rented or traded or sold to pay debts. On the other hand, Abolitionists in the North thought that slavery was something wrong and cruel. They wanted to end the slavery and set slaves free, so they started to convince people of that. When the South knew about it, they were fearful that their way of life would come to an end.  

Crops:

The economies of many northern states had moved away from farming to industry. So, they no longer needed slaves and they started to support slave’s freedom. however, the South’s economy was based on a system of large-scale farming that depended on the labor of black slaves to grow certain crops, especially cotton and tobacco.

The Abolitionist movement:

It was an effort to end slavery in a nation that valued personal freedom. They, also, wanted to the end of racial discrimination and segregation. Abolitionists such as John Brown, Frederick Douglass, Harriet Tubman, and Harriet Beecher Stowe began to convince more and more people of the evil of slavery. Abolitionists exercised a particularly strong influence on religious life, contributing heavily to schisms that separated the Methodists and Baptists, while founding numerous independent antislavery free churches.

State:

As the United States continued to expand westward, each new state added to the country shifted the power between the North and the South. The southern states felt that the federal government was taking away their rights and powers.

Fugitive salves act:

The Fugitive Slave Acts were a pair of federal laws that allowed for the capture and return of runaway slaves within the territory of the United States. These laws brought the issue home to anti-slavery citizens in the North, as it made them and their institutions responsible for enforcing slavery. In November 1850, the Vermont legislature passed the "Habeas Corpus Law," requiring Vermont judicial and law enforcement officials to assist captured fugitive slaves