Centralization of power is a basic feature of a unitary government. In a unitary government, the central government holds most of the power, and it delegates some powers to the local governments or sub-national units. The central government can take back these delegated powers if it sees fit. This means that decisions are made by the central government and are binding on all sub-national units.
On the other hand, in a federal government, power is shared between the central government and the sub-national units, and both levels of government have their own areas of responsibility. In a confederal government, the sub-national units hold most of the power, and the central government only has limited power over them.
In a presidential government, the president is the head of the executive branch of government, while in a parliamentary government, the executive branch is led by the parliament or a prime minister chosen by the parliament. However, neither of these forms of government inherently require centralization of power.