Strong military leadership and support.
Federal government is the result of a union of states. Which, could be assumed not to be sovereign. Unitary Government is when there are no states in federation, rather the government is all (other than local needs) at national level. Thus Unitary is not Sovereign.
The similarities between unitary and federal states could be that both types of governments could be democracies. A unitary state could be democratic when the people elect the government officials, as is the case in a federal state.
Probably the best country to fit this mold would be ISRAEL, but Cyprus, Lebanon, Turkey, and Iraq could fit this description with some caveats.
republic _____ No, unitary, or centralised. A kingdom, duchy etc could just as easily fit the description in the question.
The short answer is that if the united states became a unitary state it would no longer be "united states" but rather the "united state." Perhaps some successor state occupying a portion of what was once the US could be a unitary state, but the likelihood of all the constitute parts of the US voluntarily relinquishing their legislative and administrative prerogative is minute.
It is possible, it could happen in any country.
Dictatorship
That is not the correct quote. John F. Kennedy said "Ask not what your country can do for you, but what you can do for your country."
Chaos and anarchy are a possibility.
Your country could get kicked out of the European Union if you were voted out. More than likely this won't happen though.
Unitary gov. all the power in the government is held by the central government (China and Japan)!
Advantages: FLEXIBILITY: it is easy to change and so can adapt to changing society and times DEMOCRATIC RULE: The constitution, if changed, is done so by democratically elected bodies, therefore such change is done so because of pressure by the people of the country. EFFECTIVE GOVERNMENT; Strong and effective governments are created as they are able to act as they want to better the country without being restricted by old, archaic rules. HISTORY AND TRADITION: unwritten constituions have evolved over time and gained historical authority. They have been tested and proved to be effective so all rules and laws can be trusted. Disadvantages: UNCERTAINTY: it is difficult to know exactly what the constitution says and laws are often ambiguous and unclear. It can seem as if it is made up as we go along. ELECTIVE DICTATORSHIP: if the Constitution is easily changed it could rise to the problem that democratically elected governments gain power and change the constitution to meet their needs and so form a dictatorship. WEAK PROTECTION OF RIGHTS: there is nothing forcing the government into protecting individual rights and freedoms, they theoretically can do as they please. Differences: In written constituions, the constitution is found on one single authoritative document. It is the highest law of the land and judiciable - all political bodies are subject to the law adn no one is above it. This is unlike unwritten constitutions.