So one can create a theory about migrations and that is that one migratory move by a nomadic tribe can and usually does have a ripple effect on other peoples and tribes. And in the case described above, the Huns migrating nomadically westward set off a chain reaction that led to the downfall of the Roman Empire.

The third example of nomadic migrations is the expansion of the Muslims into Europe. By the year 711, according to McKay's book, the Arab (Muslim) forces in Spain defeated the Visigothic army. The Muslims had crossed the isthmus from Africa into Europe and by 719, they had migrated into Franks Kingdom, which is where Germany is today.

Eventually the Muslims were pushed back to Spain, south of what is now the border between France and Spain, but why did the Islamic forces move from their controlling land on the Arabic Peninsula all the way up into Europe? The question...

The world of Islam spread so far so fast because of the interpretation of the Qur'an that the Muslims accepted, and that is, "jihad" (holy war) requires all believers in Islam to accept two places; a "House of Islam" for Muslims, and a "House of War" for all the others. The "jihad" being carried out today by extremist Muslim followers like bin Laden, has very much the same religious fervor as the original ancient Muslims who pushed into other nations; today, Westerners are killed by the bin Laden-led terrorists because Westerners are "infidels"; back in the 8th Century, when Islam was spreading into Europe, captured people were given a chance to convert to Islam, or be killed.