Some of the major causes were constant wars, heavy military spending, and slave labor. Constant warfare required heavy military spending. The Roman army needed more and more soldiers. The second major cause was slave labor. The number of slaves increased significantly during the first two centuries of the Roman Empire. The Romans' reliance on slave labor led to the decline of morals, values ​​and ethics. The treatment of slaves led to rebellion and several servile (slave) wars. Over the following centuries, attitudes towards slaves changed. The number of slaves decreased. Some of the main causes of Greece's decline were the constant wars and Greek colonies. Constant wars were very costly. Greek colonies around the Mediterranean knew Greek culture but were not faithful to it.