What are some dangers once slaves reach a northern city?

Once slaves reach a northern city, they aren't free from slave catchers.

Explanation:

Slave catchers can come and take them back from the northern city.

A southerner could be their and claim them

nuclear fission produces the atomic bomb, a weapon of mass destruction that uses power released by the splitting of atomic nuclei the fighting in iwo jima and okinawa affected the allies' pacific strategy because truman decided to drop the atomic bomb on mainland japan.