Throughout history technological developments have changed the way war has been fought.
Cannon made the large defensive castles of the middle ages obsolete. Firearms made the suits of armor worn by medieval knights worthless. Aircraft allowed nations to fight in the sky as well as on the ground, and bomb their enemies far behind any front line on the ground. Small, portable anti-aircraft systems lead to stealth technology, and also changed how bombing campaigns were carried out, and have even lead to the use of weapon equipped drones.
Your answer would be "There would need to be an equal number of free and slave states."
The Constitution prescribes that the Senate be composed of two senators from each State. There would need to be 25 slave states and 25 free states for there to be an equal number of senators from free states and slave states.
Following this news, many people feared the world was on the brink of nuclear war. However, disaster was avoided when the U.S. agreed to Soviet leader Nikita Khrushchev's (1894-1971) offer to remove the Cuban missiles in exchange for the U.S. promising not to invade Cuba.
