An especially insightful selection from The Fellowship on unity, and the power of the Dark Lord to destroy it:
‘Alas for the folly of these days!’ said Legolas. ‘Here all are enemies of the one Enemy, and yet I must walk blind, while the sun is merry in the woodland under leaves of gold!’ ‘Folly it may seem,’ said Haldir. ‘Indeed in nothing is the power of the Dark Lord more clearly shown than in the estrangement that divides all those who still oppose him.
—Tolkien, J. R. R., The Fellowship of the Ring, 2012 edition, p 339