It balanced the states with slave and non slave states by adding Missouri as a slave state and Maine as a free state.
I believe it was because it was a key source in fueling trains. That was important because the railroads were the key source in transportation of goods and communication between the states.
Because Jefferson refused to pay atributes.
He believed that paying off the pirates only led more demands, so he decided not to pay these atributes. So Tripoli declared war on the US.
