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.
In a Presidential System, the head of state and head of government tends to be the same person. In a Parliamentary System, minority groups can form third, fourth, and fifth parties and have much more influence in government than in a Presidential System where third parties are marginalized (many complexities here).