Why would the southern states gain seats in the hor after they rejoined the union?

Southern states gained seats in the House of Representatives after rejoining the Union due to the reapportionment based on population, as outlined in the U.S. Constitution. The Three-Fifths Compromise had previously allowed slave populations to be counted as three-fifths of a person, which gave these states increased representation despite their population's composition. Once the Civil War ended and these states were readmitted, the full population counts would contribute to their representation, despite the abolition of slavery. This shift reflected the demographic realities of the South and their political interests in Congress.