Article IV of the Constitution protects existing state boundaries through a consent requirement: no new state can be formed by dividing or combining parts of existing states without approval from both the affected state legislatures and Congress. This provision ensures states can't be broken apart or merged against their will, preserving the political boundaries established at admission or through subsequent agreements.
The clause emerged from the Constitutional Convention to protect the four eastern states (Connecticut, Georgia, North Carolina, and Virginia) that still held western land claims, giving them veto power over whether those territories could become separate states. Virginia consented to Kentucky's formation from its western regions in 1792, and similar consent enabled Tennessee, Maine, and West Virginia to separate from existing states.
Article IV also governs interstate relations through the Full Faith and Credit Clause, requiring states to recognize each other's public acts, records, and judicial proceedings, and the Privileges and Immunities Clause, which prevents states from discriminating against out-of-state residents in fundamental rights like travel, trade, and economic activity.