“Tribalism is the most powerful force in the world.”

"The Philippines: A Century Hence"

1990s, A Distinctly American Internationalism (November 1999)

Source: God Is Red (1973), p. 210

Source: Lover Revealed

Variants: "... is man’s greatest invention" and "... is the eighth wonder of the world".
May add: "He who understands it, earns it; he who doesn’t, pays it."
This Snopes article http://www.snopes.com/quotes/einstein/interest.asp concluded that its status was uncertain, while this post from The Quote Investigator http://quoteinvestigator.com/2011/10/31/compound-interest/ concludes it is most likely a false attribution, since variants of the quote date back to at least 1916, with the early variants not being attributed to Einstein.
Disputed

1950s, Loving Your Enemies (Christmas 1957)
Context: Love is the most durable power in the world. This creative force, so beautifully exemplified in the life of our Christ, is the most potent instrument available in mankind's quest for peace and security. Napoleon Bonaparte, the great military genius, looking back over his years of conquest, is reported to have said: "Alexander, Caesar, Charlemagne and I have built great empires. But upon what did they depend? They depended on force. But centuries ago Jesus started an empire that was built on love, and even to this day millions will die for him." Who can doubt the veracity of these words. The great military leaders of the past have gone, their empires have crumbled and burned to ashes. But the empire of Jesus, built solidly and majestically on the foundation of love, is still growing. It started with a small group of dedicated men, who, through the inspiration of their Lord, were able to shake the hinges form the gates of the Roman Empire, and carry the gospel into all the world. Today the vast earthly kingdom of Christ numbers more than 900,000,000 and covers every land and tribe.

Source: City of Fallen Angels