How was the issue of slavery decided in the territories ceded by Mexico

They decided by making the people vote which one they wanted to be a slavery territory or a free territory.

"The new states' constitutions permitted slavery."

In 1846 and 1848, The cession of regions dissipated by Mexico are the regions that Mexico was compelled to capitulate to the United States to terminate the militant control of the nation among as an outgrowth of the Mexican-American conflict. This cession was formalized throughout the Treaty of Guadalupe Hidalgo, signaled in the center of the corresponding title on February 2, 1848 which permitted the continuation of slavery in Mexican territories.