re: #55 wheat-dogg
The North understandably did not want the 3/5ths rule to be extended into the new territories and states, because it had already given the slaveholding states more representation in the House than they would have gotten otherwise. Allowing the new areas to be slaveholding states would have meant slavery would be a near-permanent fixture in the USA — or at least a longer lasting fixture.
The settlers in the territories who brought their slaves with them also saw their property rights as having precedence over any state laws concerning slavery, which would have resulted in the de facto expansion of slavery everywhere they settled.