What makes the US constitution unique?

The United State constitution is the most basic law. All other laws (local, state...) must be agreed by U.S. Constitution.

Congress called a secret meeting in Philadelphia in 1787 to revise the Articles of Confederation. It wrote a new Constitution, which was adopted in 1789. The reason why the congress wanted to revise the Articles of Confederation is that the rules were really old.

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One factor that really shaped America is Constitution. The important part of the constitution is the separation of power which means that corruption can not happened because of the equal separation of government: legislative, executive and judicial. Each branch has some power over the others, this system is called Check Balances.

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Gradually, there were other states which were admitted in the Union: Vermont, Kentucky, Tennessee, Ohio. In 1803 Louisiana was bought from France.  

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The disputes continue in the field of Navy trade. The division of territory and spheres of influence in North America between the United States and the United Kingdom led to the British-American War (sometimes called the Second War of Independence) (1812-1814). 

The American colonies declared war in 1812 in the belief that they can use the United Kingdom being busy with Frances to win a war. Britain was ,at war with Napoleon (France), and they hoped that the American colonists could take the rest of the British domination out of North America. The colonists invasion into Canada was a total fiasco and the United Kingdom began to move other forces to America. The British did not want to start another war because they were not willing to invest additional resources in such an uncertain enterprise, which would attempt to retake North America. At the end, both sides agreed to return to the status quo and make an agreement for addressing to the biggest controversy.