Question

What was the name of the proposed law that would be slavery in all territory won in Mexico America war

Answer 1

The name of that law was Wilmot Proviso.
It was created in 1846 by Congressman David Wilmot, who thought slavery was unconstitutional. He proposed this law to the House of Representatives, but given that it mostly consisted of Southern states (who were pro-slavery), it failed initially. It was accepted the following year, however it wasn't actually enforced until the Compromise of 1850.