The first year of the Muslim calendar (ie Year 1) wasn't the birth of Mohammed or his early teachings but the migration and violent subjugation of Medina in 622, which demonstrates just how important Medina is in the whole Islamic expansion story.
The Muslims have a folk song all about this invasion, and its been sung a number of times by Westerners to welcome "new migrants" to the West. Its basically a song thanking Allah for giving them new lands.
