This may come as a surprise, but for the most part powerful governments really, really, really don't like giving up their power.

Missouri in many ways was a gut check on whether the federal government could relinquish some of its power. The answer, as is often the case, was a little yes and no.

It's never outright stated or brought up, but the fundamental worry for opponents of Missouri statehood (other than the expansion of slavery) was that self-determination would set a dangerous precedent that would weaken the U.S. Constitution's Supremacy Clause. This clause was the lynchpin of the Constitution, and what made it an improvement over the useless Articles of Confederation.

It states that in all matters, the Federal government has final say. Period. If Missouri was allowed to write up its own constitution willy-nilly, without being subject to the Federal government, it could've spelled disaster for the future of the Union.

On the other hand, in the very same bill Congress waved its legal wand and literally cut the country in half along slave and free lines. So maybe this supremacy thing has some drawbacks.