Federalism is a system of government in which governmental powers are shared among the different tiers ofgovernment in which each tieris coordinate, independent, and exclusive in its own sphere of authority (O’Connor, amp. Sabato, 2001). Separation of powers is a doctrine propounded by Baron de Montesquieu which stipulates that in order to avoid arbitrary use of state power, power should be separated and shared among the organs of government such that no organ becomes stronger than the other(O’Connor, amp. Sabato, 2001). But over the years it has been discovered that these principles have not lived up to its expectation because America had presidents who were overwhelming and dominates the legislature. A vivid example is President George Bush, after the September 11 Al-Qaeda masterminded terrorist attack on the World Trade Centre, the president presented a bill to the congress to invade Iraq. Before the house could pass the bill he had sent troops to wage war in Iraq. This was contrary to the constitutional provisions which state that before the United States would engage in a war, it must be ratified by the congress in a joint session. The overwhelming influence of the president has this principle ineffective. In the light of this,is the principle of checks and balances which states that an organ of government should act as a watchdog on the other organs of government so as to curb their excesses. In America, checks and balances have shown the relationship and interaction between the executive and other arms of government (O’Connor, amp. Sabato, 2001). As the executive relies on the legislature to pass a billhe wants to become law, the legislature can either veto the bill if considered wrong or pass and send back to the executive for assent. The executive too acts as a check by refusing to give assent to bills considered as unlawful by the legislature. The judiciary can also checkmate the activities of both the executive and legislature through a process of judicial review and regard all laws or action null and void if perceived as unlawful. The American federal structure allows for state power to be shared between the central, state, and municipal governments in such a way that each state has its own constitution where it derives its powers. Although when such laws clash with the national constitution the latter prevails. This has made the sustainability of the American values possible. For example, state police is an integral part of the American federal structure which has made security in the United States effective. Another example is the existence of the state supreme court that has made judicial and legal proceedings exemplary. Thus, Federalism has been the major factor sustaining the American values as it has its functionality in both the principle of separation of powers and checks and balances.