why and how did islam triumph over Zoroastrianism?

From a historical point of view what would you attribute Islams success over Zoroastrianism, (that is the religion of ancient Persia) ?
poly hist, does this mean that Z was absorbed by the Muslims as they re religions where somewhat similar among other reasons?

just go through this

http://en.wikipedia.org/wiki/Spread_of_Islam#Iraq.2C_Persia.2C_and_Central_Asia

Islam was never in competition with Zoroastrianism. Zoroastrianism was pretty much dead by the time of Muhammad. There were, however, tribal gods and a polytheistic religion in Arabia at the time of Muhammad that he had to overcome.

One of the ways he did this was to go into the Qabba at Makkah (Mecca) and destroy the various idols of all the gods that the Arabians had worshiped. He also built an army behind him after he was thrown out of Madinah (Medina) and marched back on the city.

You also have to remember that this was a totally different time period and people were more open to religious ideals than the scientific theories that we are accustomed to today. If someone claimed that they had spoken to God or Allah, they would be much more believable back then than they would today. Keeping that in mind, it is easier to see how Muhammad gathered such a large following by the time of his death and how Islam has spread throughout the world.

the question that you have to ask yourself is whether Zoroasterianism died or whether it was incorporated into Islam as well as Christianity. If it was incorporated into those two contemporary religions, they Z is very much alive and well.

Zoroasterianism taught that there was an eternal fight between good and evil. That denotes, at least to me, that there exists a dualism in the god structure - two gods of pretty near equal strength. Both Christianity and Islam teach the same thing. We know that Christianity was heavily influenced by Z and since Islam, which came 5-6 centuries after Christianity is influenced by the New Testament also, Islam was influenced by Z.

The Wise Men of the Christmas story were Zoroasterian