Question

Why did Southern states fear Missouri’s entry into the Union as a free state?

Answer 1

They did not want free states to have a majority in the Senate.

Answer 2

The main reason why many Southern states feared Missouri’s entry into the Union as a free state was they they were afraid such an admission would mean that the institution of slavery would eventually die out in the South--as more people in free states found ways to bolster their economies without the help of slavery.