There are in excess of 1.5 billion Muslims in the world. The great bulk of this population lives in South and Southeast Asia, where Muslims constitute the largest religious group. States with Muslim population majorities are often called Muslim states, regardless of the system of government and political system. But there are also significant Muslim populations in other states. Population movement in the second half of the twentieth century has led to the growth of Muslim communities in Europe, the US and Australia. Muslim migration to Europe seems to have closely reflected colonial links, so that the biggest Muslim community in the UK is from South Asia where the British Empire held sway, while Muslims from Algeria constitute a significant community in France. This picture, however, is fast evolving and Muslim minority groups in non-Muslim states are becoming increasingly heterogeneous in ethnic background and creed.
The demographic spread of Muslims has led to some key questions about identity, community and citizenship. Islam emerged in the Arabian Peninsula in the seventh century, but was not tied to that geography.