What were the most important factors that contributed to Barack Obama's election in 2008?

The population was dissatisfied with the Republican policies and the promises Obama made had been very enticing.

Explanation:

Obama was an unlikely president in spite of his long winded political career and savvy politics not the least because of his skin color and the nature of the country at the time in the middle of a long winded war on terror that did not look like it was going to end any time soon.

Obama was elected as a polar opposite alternative to the President Bush who had not made the people satisfied with his efforts and the country seemed to be in a huge crisis in his time.