The Mexican War of 1846-1848 secured a vast new territory (from Texas west to California, north to Washington State, and encompassing the states of Oregon, Idaho, Nevada, and Colorado). The settlenent of border issues with Great Britain established the continental border line at 49 degrees North latitude. The critical question left unresolved (except for California) was whether enslaved labor would be permitted in territories that would later become the states of Utah, New Mexico, and Arizona. What was the economic rationale for leaving the question unresolved?

		The political power of the rich slave-owning cotton producers of the South was balanced by the political power of the anti-slavery elected officials of the North. There was a political stalemate that the US President and Congress attempted to resolve with the Compromise of 1850, but the issue was not resolved until the Civil War.
		There was no lack of resolution, but except for the newly-acquired territory of Texas, there was no cotton cultivation, and thuse no cotton-centered economic activity, in California, Arizona, New Mexico, Colorado, nor in any areas north.
		There had always been a version of the 1850 Fugitive Slave Act -- even in the Northwest Ordinance of 1787 -- so enslaved humans were an economic consideration even for states and territories where slavery was banned (e.g., the northern states plus California, Oregon, Washington, Idaho, and the territories that would become Wyoming, North and South Dakota, Nevada, and Colorado.
		All of the above.