Mecca vs. Medina: Which Is Islam's Central City?

Mecca (Makkah) is Islam's holiest city—birthplace of the Prophet, site of the Ka'ba, and destination of Hajj.

Medina (Al-Madinah) is the first Islamic political capital. The Prophet migrated there (Hijra, 622 CE), built the first Muslim community (Ummah), and established the first mosque (Quba) and the Prophet's Mosque (Al-Masjid an-Nabawi).

Clarification

The question's premise is slightly off: Mecca was never "established as the central Islamic city" in a political sense; it has always been the spiritual center. Medina served as the early caliphate's administrative hub.