Iran

Shura, as done during early Islamic history, is not the same thing as modern voting, a modern parliament, or modern democracy. Modern democracy developed recently in history, and some Muslims back-project it and claim it has roots in Islam by saying it is like shura. However, modern democracy is different from shura, and this is not an accurate analogy; rather, it is a form of apologetics.

In any case, the Shii belief is that the succession to the Prophet (S) was appointed by Allah and people did not have the right to choose it - neither by shura nor by a one-person-one-vote system - just as people do not have the right to choose how many times a day they say formal prayers, or what month to fast in.

However, Allah has not appointed specific individuals to be our political leaders presently, so we use other systems of governance and selection of leaders.

Furthermore, when you read the history of what actually happened during the selection of the first three caliphs, you see that some things happened that were questionable or politically motivated for an agenda, and it was not that everyone got together and simply discussed with sincerity and equality who should be the next leader. The scenario was different for each caliph. When you read what happened, you see it is nothing like voting today where every person has a single vote and the majority wins. You can look into that in history books.

First, in this day and age, it is good for us to be thoughtful about how we phrase things. "Liberating" people from Zoroastrianism is rude. Zoroastrianism, like most world religions, has good things and bad things. In any case, it is good to respect people's faith and heritage, especially since Zoroastrianism continues to be practiced today.

Second, describing the conquest of lands by the Muslim Empire as "liberation" can come across the wrong way.

It is true that 'Umar ibn al-Khattab ordered an invasion of the Sassanian Empire which led to the conquest of what is present-day Iran. So, it is more correct to say that he annexed Iran to the Arab-Muslim Empire, and this was one of the factors that led Iran to become a Muslim region.

That being said, military annexation of a region is not the same thing as converting a people to Islam, or even introducing them to Islam. Actual conversion to Islam in conquered lands happened over a span of time. Conversely, Islam spread in many areas, such as Indonesia, where the initial Muslim Empire had no power. There were good and bad points about the conquests of the early Muslim Empire.

Sometimes - in my experience - some of our Sunni brothers and sisters glorify those conquests, perhaps out of respect for the first 3 caliphs, without taking into consideration that they were in fact military conquests which were not dissimilar to the expansion of other empires. Like other military expansions they brought some good and and some difficulty, some people in these areas were (according to what we can glean from historical records) fine with being under Muslim rule or even welcomed it, and some resisted it. Basically it's good to take a more intermediate position, neither to say "Islam spread by the sword and those Muslims are violent!" nor to say "Muslims liberated all the other regions from their former faiths." (In fact, that comes across as quite violent.) 

As for who introduced Iran to Islam, why not begin with Salman al-Farsi? And, second, what about the letter that the Prophet (S) sent to the Persian king, inviting him to Islam?