If US States Were Individual Countries. {By GDP}

Top Countries by GDP

United States                          16,244,600

China                                        8,227,103

Japan                                        5,961,066

Germany                                  3,425,928

France                                      2,611,200

United Kingdom                      2,475,782

Brazil                                       2,252,664

Russia                                      2,014,775

Italy                                          2,013,375

California                                1,958,904

India                                         1,858,740

Canada                                     1,779,635

Australia                                   1,532,408

Spain                                        1,322,115

Texas                                        1,308,132

Mexico                                     1,178,126

New York                                1,157,969

South Korea                             1,129,598

Where the rest of our top 10 states with highest GDP would rank in the world if they were individual countries.

Florida {17-Between Indonesia and Turkey}

Illinois  {19-Between the Netherlands and Saudi Arabia}

Pennsylvania  {20-Between Saudi Arabia and Switzerland}

Ohio     {22-Between Iran and Sweden}

New Jersey {23-Between Ohio and Sweden}

North Carolina  {24-Between Norway and Poland}

Virginia {26-Between Belgium and Argentina}

Mississippi is by any measures one of the poorest states in the US but it actually ranks 35th by GDP and would be the 60th wealthiest country in the world if it were an independent nation.  If the states that comprised the old Confederacy were an independent nation, they would have the 4th largest economy in the world {that assumes their growth trajectories had remained the same}.

The genius of the American system is that each of these states is part of a larger whole.  Not only are there no barriers to entry among states but our federal system means these states don't have to replicate all the  infrastructure of a sovereign nation.  No state for example needs to have it's own postal service or foreign office.  Most importantly no state in our system has to have its own military.

Source: Peter G. Peterson Foundation.

We spend more on defense then the combined purchases of the next eight countries but each state's share of that is much less on a percentage basis then if they had to build their own.

Source:  Wikipedia.