“Why travel if all the world is coming to Aleppo, the capital of it all?” says a character in Khaled Khalifa’s spacious historical novel “No One Prayed Over Their Graves.” This is the Aleppo of the Ottoman Empire at the turn of the 20th century, a teeming commercial entrepot and cross-cultural hub where Muslims, Christians and Jews fractiously but profitably coexisted. Set between 1881 and 1951 and following the waning fortunes of two families, the novel reads at times like a love letter to the Syrian city where Mr. Khalifa grew up, and at times like a eulogy…