The structure of Congress under the Articles of Confederation was unicameral: each state had between two and seven congressmen, depending on state's population, and was appointed directly by each state legislature.
This structure favored the most populated states such as Pennsylvania over the least populated, because the more populated a state, the more delegates it could send to Congress.
When the US Constitution was ratified, Congress became bicameral mainly for two reasons:
To give both the most populated states and the least populated states fair representation. This was achieved by implementing the Connecticut Compromise: The Senate was meant to equally favor each state, regarless of population, thus, each state was entitled to two senators. And The House was designed to favor the most populated states: House representatives are proportional to population.
To further the development of checks and balances. A unicameral Congress is more powerful than a bicameral Congress. Both House and the Senate have some specific powers, but for most issues, they have to work together. This avoids concentration of power.
These two points can be thought of as the advantages the US Congress under the current constitution has over the previous Congress under the Articles of Confederation.
Explanation: From Wikipedia.com; "Greek democracy created at Athens was direct, rather than representative: any adult male citizen over the age of 20 could take part, and it was a duty to do so."
The port status was not free. This meant that taxes had to be imposed on goods and services, making it more expensive for both the producers and consumers.
