Thank you for your question. The Imam (af) cannot act to his full effectiveness without the support of the Ummah itself and so it is the Ummah that has chosen this situation for itself. In the same way, the Imams could not prevent the cruelty of the Ummayid and Abbasid dynasties or the injustice of some of the prior leaders as these are the leaders that the Ummah had chosen for themselves in rejecting the leadership of the Imams (as). The injustice in this time is a natural consequence of the physical absence of the Imam (af).
May you always be successful.