The growth of Christianity throughout history has been steady, but not linear. It has grown in spurts, with seasons of expansion and seasons of contraction. There are many contributing factors to this pattern, but one of largest is the rise and fall of empires which bring with them relative peace, prosperity, and stability. There have been four of these "Unipolar" seasons in the last two millennia: The Pax Romana, The Pax Mongolica, the Pax Britannica, and now the Pax Americana, which is already waning. When empires fall, the world is plunged into "Multipolar" seasons of conflict and war, which hinders world missions due to geopolitical and economic factors.