Simplify the following text for a Grade 7 native English-speaking person.
Original: In 1815 at the Congress of Vienna the Final Act only recognized 39 sovereign states in the European diplomatic system , and as a result it was firmly established that in future new states would have to be recognized by other states , and that meant in practice recognition by one or more of the great powers .
Simplified: In 1815 at the Congress of Vienna the Final Act only recognized 39 sovereign states in Europe . Because of this , they said that in future new states would have to be recognized by other states .