How people will believe the Mahdi:
Of all the Children of Israel or the Israelites in the time of Jesus Christ... out of all them, only 12 men believed: one of them betrayed him. And these 12 doubted Jesus Christ in spite of all the miracles he did.
So of all people in the entire world, only a few will believe the Mahdi when he comes.
Therefore, it is not strange or weird that you do not believe, but mock and ridicule like the past nations who mocked their messengers.
In spite of that Muslims have the Quran, they do not believe his interpretation of the Quran and his call to the devotion to God alone; because they follow their fathers and their sects like you yourselves.
Because it is narrated that "Prophet Mohammed was denied about the Quran revelation, while the Mahdi will be denied about the interpretation."
It means: People say to Prophet Mohammed: this Quran is not from God, and in the same way people will say to the Mhadi this is not the correct interpretation, which is not from God.
Moreover, in spite of that many people respected his interpretation, but very few followed him.
So he was denied, as had God's messengers and prophets denied before, like Moses had been denied, and like Noah, Abraham, Lot, the tribes of Aad, and Thamood, and in fact, all the past nations denied their prophets at the start, with the exception of Jonah's people of Nineveh who believed and were spared the punishment.
The Mahdi will come when disbelief and idolatry prevail, and Muslims will be overcome everywhere which has been fulfilled: and Muslims are overcome everywhere, and all sects and states have been set on them: Jews, Christians, Hindus, Buddhists and Communists, and Muslims have been victims everywhere in the world.
Then how could you believe, while you are not Muslims, and you follow your culture and follow your people's traditions unless God wills to guide whomever He pleases? While Muslims themselves deny the Mahdi.
So it is only if God Himself obliges the world to submit!!! or to believe??
What I understood of the Mahdi ruling is what Abu Abd-Allah saw in his dream;
He asked God: How can I rule when Muslims do not follow me, and when the power is by the hand of unbelievers?
He saw a rascal on a bridge and he transgresses on people right and left and people go away from him and cannot do anything to him.
He said: I came direct to that man and merely once I touched him, he fell in the water and statred jerking and at last was drowned.
The people there came and said to me: God bless you! You have ridden us from this rascal, and they gathered together counseling each other (they wore different dress styles of the Arabs) then they came to me and said: You rid us from this rascal and we will make you our king.
The angel came and interpreted the dream to me: "The rascal is the Zionist Jews and God will give you victory over them, and the Arab will make you their king. So in this way, you will rule."