Final answer:
Approval to merge Alabama and Mississippi would need to come from the state legislatures of both states, Congress, and possibly the citizens through a referendum.
Step-by-step explanation:
To merge Alabama and Mississippi into one state, several key votes would be necessary due to the complexity of turning two existing states into a single political entity. Firstly, the state legislatures of both Alabama and Mississippi would need to vote in favor of the merger. Following state-level approval, the proposal would require a national-level sanction; thus, Congress would have to pass legislation approving the union of the two states into one. Additionally, it is likely that the plan would need to be presented to the people of both states in the form of a referendum, where citizens can cast their direct votes on such a significant change. Hence, agreement from a majority of voters in Alabama and Mississippi would be essential.
It should be noted that such a process would be unprecedented and complex, as the U.S. Constitution does not directly outline procedures for merging states. Historical contexts, such as voting rights issues in the Deep South during the Civil Rights era and periods of secession and reunification, highlight the profundity of any movement to alter state boundaries or governance. The process of state merger would engage deeply with issues of regional identity, representation, and the historical dynamics of the United States' political structure.