Every northern state had either outlawed the practice or had a defined timeline to emancipation. ZERO southern states could say the same.
Abraham Lincoln, First Inaugural Address: "I have no purpose directly or indirectly to interfere with the institution of slavery in the states where it exists. I believe I have no lawful right to do so, and I have no inclination to do so."
Lincoln spoke those words to assure the southern states that they didn't need to do anything stupid. They did it anyway.