The Constitution of the United States is the supreme law of the United States of America. It superseded the Articles of Confederation, the nation's first constitution, in 1789. Originally comprising seven articles, it delineates the national frame and constraints of government. The Constitution's first three articles embody the doctrine of the separation of powers, whereby the federal government is divided into three branches: the legislative, consisting of the bicameral Congress (Article I); the executive, consisting of the president and subordinate officers (Article II); and the judicial, consisting of the Supreme Court and other federal courts (Article III). Article IV, Article V, and Article VI embody concepts of federalism, describing the rights and responsibilities of state governments, the states in relationship to the federal government, and the shared process of constitutional amendment. Article VII establishes the procedure subsequently used by the 13 states to ratify it. The Constitution of the United States is the oldest and longest-standing written and codified national constitution in force in the world today. The drafting of the Constitution, referred to as its framing, was completed at the Constitutional Convention that took place in Philadelphia in 1787 from late May through mid-September. Delegates to the convention, chosen by the legislatures of 12 states (Rhode Island refused to send delegates), either were members of state legislatures or were appointed by the legislatures. The convention's initial mandate was limited to amending the Articles of Confederation, which had proven highly ineffective in meeting the young nation's needs. Almost immediately, however, delegates began considering measures to replace the Articles. The first proposal discussed, introduced by delegates from Virginia, called for a bicameral (two-house) Congress that was to be elected on a proportional basis based on state population, an elected chief executive, and an appointed judicial branch. An alternative to the Virginia Plan, known as the New Jersey Plan, also called for an elected executive but retained the legislative structure created by the Articles, a unicameral Congress where all states had one vote. The defeat of the New Jersey Plan led to a series of compromises centering primarily on two issues: slavery and proportional representation. The first of these pitted Northern states, where slavery was slowly being abolished, against Southern states, whose agricultural economies depended on slave labor. The issue of proportional representation was of similar concern to less populous states, which under the Articles had the same power as larger states.