Original: After the English Civil War and the execution of Charles I , the republic 's existence was initially declared by An Act declaring England to be a Commonwealth by the Rump Parliament , on 19 May 1649 .
Simplified: After the execution of Charles I on January 30 , 1649 , the Commonwealth was declared ( An Act declaring England to be a Commonwealth ) by the Rump Parliament on May 19 , 1649 .