What ended slavery in the North?

This is an important distinction.

The Northern states generally abolished slavery through state-level gradual or immediate abolition laws, beginning during and after the American Revolution.

For example:

• Pennsylvania adopted gradual abolition in 1780.
• New York adopted gradual emancipation in 1799 and completed abolition later.
• New Jersey's gradual abolition began in 1804.

So slavery in the North did not wait for the Civil War's end.

The Thirteenth Amendment (1865) then abolished slavery throughout the United States, including the remaining slavery in the South.

So the broad sequence is:

Northern state abolition laws → gradual disappearance of slavery in the North

while:

Civil War + Emancipation Proclamation + Thirteenth Amendment → destruction of slavery in the Confederate South and constitutional abolition throughout the United States.

That is why saying simply:

“the Civil War ended slavery”

is incomplete.

The Thirteenth Amendment is the crucial constitutional abolition.