4.

Which part of the Fugitive Slave Act was the North most upset with?

California would enter the Union as a free state

Slaves escaping to the North needed to be returned to the South.

Texas and New Mexico would solve their border disputes

The Slave trade would be abolished in Washington D.C.

The part of the Fugitive Slave Act that the North was most upset with was Slaves escaping to the North needing to be returned to the South. This was seen as a violation of their states' rights and a betrayal of their moral convictions regarding slavery. Many Northerners actively resisted the law and supported fugitive slaves, which contributed to tensions between the North and South leading up to the Civil War.