Simplify the following text for a Grade 8 native English-speaking person.
Original: This work was adopted as the sole official song on May 11 , 1813 , three years after the `` May Revolution '' ; May 11 is therefore Anthem Day in Argentina .
Simplified: This song was adopted as the national anthem on May 11 , 1813 , three years before the formal declaration of independence from Spain . May 11 is therefore Anthem Day in Argentina .