Constitutional Convention (United States)

The Constitutional Convention (also known as the Philadelphia Convention) was held from May 25 to September 17, 1787 in Philadelphia, Pennsylvania. Although the Convention was called to revise the Articles of Confederation, it became clear from the beginning that many members, including James Madison and Alexander Hamilton, intended to create a new government rather than fix the existing one. The delegates elected George Washington to preside over the Convention. The result of the Convention was the creation of the United States Constitution. This makes the meeting one of the most significant events in the history of the United States.
Debates
Most of the disputes were about the makeup and election of the Senate. Other disagreements concerned how "proportional representation" was to be defined (whether to include slaves or other property). They needed to decide whether to divide the executive power between three persons or invest the power into a single president. They also had to work out how to elect the president, how long his term was to be and whether he could stand for reelection. There were issues over what offenses should be impeachable. Most of the time during the Convention was spent on deciding these issues, while the powers of legislature, executive, and judiciary were not heavily disputed. Once the Convention began, the delegates first agreed on the principles of the Convention, then they agreed on Madison's Virginia Plan and began to modify it. A Committee of Detail assembled during the July 4 recess and produced a rough draft. Most of this rough draft remained in place, and can be found in the final version of the constitution. After the final issues were resolved, the Committee on Style produced the final version, and it was voted on and sent to the states.
The Virginia Plan
James Madison had spent the winter of 1787 making a study of various confederations throughout history. He came to Philadelphia armed with a wealth of knowledge and an idea for what the United States government should be. His plan was presented to the Convention by Edmund Randolph, the Governor of Virginia. It became the broad outline of what would be a new government under the U.S. Constitution. His plan called for three branches of government with checks and balances to prevent any one branch from abusing their power. Madison's idea for a legislature had two houses. One would feature members elected by the people for a three-year term. The other would have its members elected by the state legislatures and would serve for 7 years. Both would have the seats determined by the population of the country.
Two more plans
After debating the Virginia plan for two weeks, William Patterson presented his plan called variously, the New Jersey Plan, the Patterson Plan and the Small State Plan. It was very similar to the Articles of Confederation and featured a unicameral (one house) legislature. All states would have one vote. He had one idea that was kept; that state laws that ran counter to federal laws would be voided.
A third plan was offered by Alexander Hamilton. It was a copy of the British Constitution. It also was bicameral with an upper house and a legislature in which members served on their good behavior.
A solution
Finally they worked out a compromise between all three plans. The new government would have an upper house, having an equal number of delegates from each state, and a lower house with representation based on population. The executive branch would have most of the responsibilities of foreign affairs while other important powers, like ratifying treaties, would be the responsibility of the legislative branch. After the new Constitution was ratified by the states, it went into effect in 1789.
References
United States Constitution
1787 in the United States
18th century in Philadelphia