The Sumerians were the first people to migrate to Mesopotamia, they created a great civilization. Beginning around 5,500 years ago, the Sumerians built cities along the rivers in Lower Mesopotamia, specialized, cooperated, and made many advances in technology. The wheel, plow, and writing (a system which we call cuneiform) are examples of their achievements.
1 In a presidential system, the legislature and the executive do not have to be aligned and often work against each other. 2  Policy implementation can be much slower and more moderated, at least in the US system.
A number of key theoretical differences exist between a presidential and a parliamentary system: 1  In a presidential system, the central principle is that the legislative and executive branches of government are separate.n a full-fledged presidential system, a president is chosen directly by the people or indirectly by the winning party to be the head of the executive branch. Presidential governments make no distinction between the positions of head of state and head of government, both of which are held by the president.