Bicameralism in the U.S.
When the federal government was initially constructed, a system of two separate legislatures was designed. In this system, the seats in the lower house (United States House of Representatives) are allocated solely based on population. In the upper house (United States Senate), seats are evenly divided among the states, regardless of population (two seats per state). In what was known as the "Great Compromise," it was agreed to have both methods of seat allocation in Congress.
The following is an excerpt from John Adam's "Notes on Debates in Congress" as the issue was being debated:
|“||If We vote by Colonies, this Method will be liable to great Inequality and Injustice, for 5 small Colonies, with 100,000 People in each may outvote 4 large ones, each of which has 500,000 Inhabitants. If We vote by the Poll, some Colonies have more than their Proportion of Members, and others have less. If We vote by Interests, it will be attended with insuperable Difficulties, to ascertain the true Importance of each Colony.--Is the Weight of a Colony to be ascertained by the Number of Inhabitants merely--or by the Amount of their Trade, the Quantity of their Exports and Imports, or by any compound Ratio of both.||”|
—John Adams, 
There was also a basic desire to have two separate legislative bodies rather than one. As outlined by James Madison in The Federalist No. 63:
|“||The people can never willfully betray their own interests; but they may possibly be betrayed by the representatives of the people; and the danger will be evidently greater where the whole legislative trust is lodged in the hands of one body of men, than where the concurrence of separate and dissimilar bodies is required in every public act.||”|
—James Madison, Federalist 63, 
- Note: This text is quoted verbatim from the original source. Any inconsistencies are attributed to the original source.
- http://press-pubs.uchicago.edu/founders/print_documents/v1ch12s3.html The Founders' Constitution, "Bicameralism," accessed August 4, 2014
- http://www.constitution.org/fed/federa63.htm The Federalist No. 63, "The Senate," March 1, 1788