Why were the Mormons driven from Illinois in 1845?

The people of Illinois were not happy with the huge influx of people into their state. They went to Illinois to live on the 'frontier', and now huge numbers of easterners and Europeans were coming and taking over their land and culture. The Mormon headquarters, Nauvoo, was one of the biggest cities in the state at the time and the huge number of Mormons in the state was influencing the state politics enough that people got angry at that as well.