Was the Mahdi’s mission a success if Muslims are so divided today?

No prophet changes people against their will. The measure is whether those who accept him are changed, and the mission of the Mahdi can be judged by that too.

The question assumes that the Mahdi would have to bring peace to the world as if with a magic wand. This assumption contradicts the whole history of religion. God sends a messenger to give people an opportunity. Those who accept it benefit from it. Those who reject it are not forced, as the verses above show.

One can put the same question about the time of the Holy Prophet Muhammad (saw). The condition of many Muslims has also declined since then. No one would conclude from this that his mission failed. With him one can see what really counts. The Arabs who accepted him went through a profound change of character. In the same way Jesus (as) transformed the people who followed him. They learned to forgive and gave up revenge. He himself said that a tree is known by its fruit.

So the only valid measure is whether the people who accept the messenger are changed. This includes a readiness to make sacrifices for a good cause. The early Christians held on to their faith for generations, even though they were persecuted.

The Ahmadiyya Muslim Jamaat can be looked at by the same measure. In some countries its members are persecuted simply for declaring that there is no god but Allah and that Muhammad (saw) is His Messenger. The first Muslims in Mecca went through something similar. Even so, they hold on to their faith and strive for good character. It is not yet perfect, but the striving is genuine. Anyone who compares honestly can judge for themselves.