Christianity's doctrines preached peace and unity, which caused Rome's armies to be considerably less fierce and effective
<span>In The Communist Manifesto, Karl Marx and Friedrich Engels laid foundation for the Communist ideology. They encouraged workers to take control of their own destiny instead of allowing the management to control workers like a class of slaves. At the end of the book, Marx and Engels called workers to rise up together with the rallying cry of "Workers of all countries, unite!" Therefore, the correct answer is A. The Communist Manifesto.</span>
