Final answer:
Article 6 of the Northwest Ordinance prohibited slavery in new territories, a provision not present in the Tallmadge Amendment, which caused a North-South divide and almost led to disunion.
Step-by-step explanation:
Article 6 of the Northwest Ordinance outlined the conditions under which the Western Territories would be organized and admitted to the Union. One significant aspect not included in the Tallmadge Amendment was the prohibition of slavery in these territories. The Tallmadge Amendment, proposed in 1819, sought to restrict the expansion of slavery into Missouri and provided for the gradual emancipation of slaves already there. The amendment caused a sectional split, with the North supporting and the South opposing it. The difference between the Ordinance and the Amendment reflects the growing sectional tensions that nearly led to disunion decades before the Civil War.