Because Islam continued to give a disciplined way of life...
Because Islam continued to give a disciplined way of life and progressed during the lifetime of the Prophet and because all the departments of this Islamic state functioned under the divine guidance of the Holy Prophet, it was suitable, rather utmost necessary that after the passing away of the Holy Prophet (s.a.w) the reins of the kingdom should remain in the hands of those impeccable Imams who were the divine representatives after the Messenger of Allah (s.a.w), and who were appointed by Almighty Allah.
This method would have saved Islam from distortion and would have established it on a firm foundation forever. In this way Islam would have remained free from the claws of materialist proud rulers and it would have remained pure of the emotional ups and downs of the kings and Emirs and their unwarranted zeal and nuances.
This was the reason that the Holy Messenger declared, on the basis of the specific directions of the Almighty, that after him there would be twelve Imams, and he also informed that, “Of whosoever I am the master, this ‘Ali is also his master.” This step was taken so that Islamic Shariah may not be sacrificed at the altar of political intrigues.
However, some people, whose aspirations did not discriminate lawfulness and illegality, did not like this, and they deemed it such that rulership should not remain in the hands of ‘Ali and his successors. In this way Islam was forever deprived of the security that was bestowed upon it by Allah. As a result Islam became a target of all those ills that had befallen the previous religions. Why Islam became a target of destruction It is very painful to write on this subject.
However, if we are able to survey the past without any bias and bigotry it would be a very firm step for benefit of our future guidance. I have heard people expressing astonishment that how could a person like Yazid acquire the rulership of Islamic dominions? What created a favorable atmosphere for such an eventuality? Nothing in this world happens without a cause.
Those who were flowing in the current of the events may not have realized the importance of each and every incident, but when we consider those events today we can place each and every incident in a proper perspective. And our judgment would be more correct than the judgment of those who had practically acted in that drama.