Answer: increase in manufacturing
The Articles of Confederation was an agreement a that served as the first constitution. They stablished the Central government and gave it limited powers like those of Parlament. While the American states grew, the limitations of the Central Goverment were apparent and showed it was weak and unable to govern them efficiently. The result was individual requests for changes to the Articles, ultimately it became the Federal Government under the Constitution.
This is because of proportional representation.
The legislature is composed of the Senate and the House of Representatives. The Senate is considered the state's house, and elects the same number of representatives for each state, so as to maintain the equality of states in their demands.
However, the house of representatives elects deputies in a proportional way, that is, the states with the highest population density elect more representatives than the less populous states. It is a reasonable measure that maintains the proportionality of representation.