Final answer:
The most supported conclusion of the debate over land grants in New Mexico is the political implications, as these were closely tied to the national debate over slavery expansion and related economic concerns.
Step-by-step explanation:
The conclusion best supported by the ongoing debate over land grants in New Mexico is D) Political implications. Throughout the mid-19th century, following the approval of the Treaty of Guadalupe Hidalgo in 1848, discussions around land expansion were closely tied to the contentious issue of slavery. Northerners and Southerners in the United States held divergent views on allowing slavery in new territories, such as California and New Mexico.
These debates were less about humanitarian concerns and more concerned with the economic and political implications of the expansion of slavery, which included land grants in New Mexico. The disagreement contributed to national political tensions, eventually leading to the Compromise of 1850 and later the succession of southern states, propelling the nation toward the Civil War.