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With respect to the importation of slaves it was left to Congress. This disturbed the 2 Southernmost states who knew that Congress would immediately suppress the importation of slaves. Those 2 states therefore struck up a bargain with the 3 New England states. If they would join to admit slaves for some years, the 2 Southernmost states would join in changing the clause which required 2/3 of the legislature in any vote. It was done. These articles were changed accordingly, and from that moment the 2 Southern states and the 3 Northern ones joined Pennsylvania, New Jersey and Delaware, and made the majority 8 to 3 against us instead of 8 to 3 for us as it had been through the whole Convention. Under this coalition, the great principles of the Constitution were changed in the last days of the Convention.
— GEORGE MASON