Where are the major areas of settlement for the religions: Islam, Judaism, and Christianity?
Great answer above. A few other details as far as where these religions are found:
95% of the world's Jews live in either Israel or the United States, with considerably more in the United States. It is a very small religion though, with an estimated 16 million followers worldwide.
While the Arabian Peninsula is considered the birthplace of Islam, relatively few people live there. It is still considered the center of the religion since it is Mohammed's holy land, but by far, Asian Muslims outnumber Arabian and African Muslims. There are more than a billion Muslims worldwide, including over 6 million in the US.
Christianity spread along with the Christian empires of Europe. They believed it their duty to be missionaries to the native peoples of the lands they conquered, and were very successful in doing so. For example, nearly 100% of Latin America is Roman Catholic.
These religions are no longer really confined to their original areas of settlement and they are all really world religions now with followers everywhere. However, there are some major areas of concentration.
Muslims are concentrated for the most part in Asia and Africa. The ancestral homeland of Islam was the Middle East and Saudi Arabia in particular. Nowadays, however, the most populous Muslim country is Indonesia and many countries in Africa are predominately Muslim.
Jews, of course, make up much of the population of Israel. Since the Holocaust, the other major center of Jewish population is the United States.
Christians can be found on every inhabited continent in large numbers. Each continent has at least one country that is predominately Christian.