Original: Since Minamoto no Yoritomo launched the shogunate, the true power had been in the hand of the Shoguns, who were mistaken several times for the Emperors of Japan by western countries.
Simplified: Since Minamoto no Yoritomo started the shogunate, the true power had been in the hand of the Shoguns, who were mistaken several times for the Emperors of Japan by the Chinese government.