How was this section of the 14th amendment significant to reconstruction?

Question

Section 2. Representatives shall be apportioned among the several States according to their respective numbers, counting the whole number of persons in each State, excluding Indians not taxed., all slaves are now counted as a whole person for purposes of representation and taxation, whereas they were counted as three-fifths a person while slavery was intact. This vastly increased the Congressional representation of the southern states, threatening the northern stranglehold of power during the Civil War.

Answer 1

What is unclear about this?

"...vastly increased the Congressional representation of the southern states, threatening the northern stranglehold of power..."

"representation" = number of congressmen in the House of Representatives