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 parliamentary republic is a system in which a prime minister is the active head of the executive branch of government and also leader of the legislature. The president's degree of executive power may range from being reasonably significant (e.g. Pakistan) to little (e.g. India) or none at all (e.g. Ireland).