The Western Roman Empire lasted for about 1,000 years, which is astonishing given the vast number of existential threats that Rome faced, which eventually toppled it. As detailed at American Greatness.com, Rome successfully, at least for a considerable period of time, assimilated diverse ethnicities into Roman society, in a grand melting pot. This, no doubt forms an inspiration to mass immigration supporters today. Yet, the key here is assimilation, not multiculturalism. It was only when Roman began to permit the ethnicities to maintain their own distinct cultures, rather than full integrating into Roman society, that cracks began to develop, but this was inevitable because after a point, the foreigners outnumbered traditional Romans. As detailed by Peter Heather in his book Empires and Barbarians (2015), mass immigration of the barbarians usually took the form of invasions; the Empire was invaded in the second century by the Marcomani, in the 4th century by the Goths, and in the 5th century by the Franks. As the number of invasions increased, the Romans moved to stop fighting them, and ceded land to them. The barbarians did not like tax, so the Roman tax base decreased. Along with other financial woes, this weakened Rome’s military, until, the entire Empire collapsed.