A Unitary State places most power in the hands of a central government. A Federal State allocates power to local units of government. A country's cultural and physical characteristics influence the evolution of that government. In principle the unitary government works best in a nation-state characterized by few internal cultural differences and a strong sense of national unity. The unitary system requires effective communication with all regions of the country.
Smaller states are more likely to adopt a unitary government.
Unitary states are especially common in Europe. In reality some multinational states have adopted unitary systems of government so the values of one nationality can be imposed on others. When the communists took control of Eastern Europe, the countries became unitary states so they could promote communist ideology. France has long been considered a good example of a Unitary state. A strong national government that dominates local government decisions.