Imagine, if you will, two scenarios...
- Western Islam: In this world, the early Muslim conquests of Byzantine territory in the Levant,. Egypt, and North Africa, as well as Visigothic Hispania, are roughly as successful as they are in our timeline. However, to the east, the Rashidun Caliphate is never able to fully defeat the Sasanian Empire, nor lay the groundwork for permanent, uncontested Muslim rule of Mesopotamia. Zoroastrianism remains the dominant religion of the Persian people, at least in the short term, and Islam never finds a significant foothold in Central, South, or Southeast Asia by war or trade. Various steppe peoples probably still mount successful invasions of much of Eurasia at some point, but none ever do so under the banner of Islam, so there is no precise equivalent of the Ottoman or Mughal empires.
- Eastern Islam: Here, the early Muslim invaders do successfully invade Persia and points east, thus establishing a firm presence for their religion throughout much of Asia and affording groups such as the Turks at least contact with it, if not conversion. However, to the west, the Muslims are never able to fully oust the Byzantine Empire from the Middle Eastern and North African holdings, and Arab armies are certainly never able to invade parts of Western Europe such as Italy or Gaul. The Franks never have the opportunity to fight any Muslims, and the Mediterranean remains a Christian lake.