Concept
The European balance of power is a tenet in international relations that no single power should be allowed to achieve hegemony over a substantial part of Europe. During much of the Modern Age, the balance was achieved by having a small number of ever-changing alliances contending for power, which culminated in the World Wars of the early 20th century. By 1945, European-led global dominance and rivalry had ended and the doctrine of European balance of power was replaced by a worldwide balance of power involving the United States and the Soviet Union as the modern superpowers. The emergence of city-states (poleis) in ancient Greece marks the beginning of classical antiquity. The two most important Greek cities, the Ionian-democratic Athens and the Dorian-aristocratic Sparta, led the successful defense of Greece against the invading Persians from the east, but then clashed against each other for supremacy in the Peloponnesian War. The Kingdom of Macedon took advantage of the following instability and established a single rule over Greece. Desire to form a universal monarchy brought Alexander the Great to annex the entire Persian Empire and begin a hellenization of the Macedonian possessions. At his death in 323 BC, his reign was divided between his successors and several hellenistic kingdoms were formed. The historical Etruscans had achieved a state system of society, with remnants of the chiefdom and tribal forms. Rome was in a sense the first Italic state, but it began as an Etruscan one. It is believed that the Etruscan government style changed from total monarchy to oligarchic republic (as the Roman Republic) in the 6th century BC. Rome expanded into the whole of Italy around the same period and then rose to prominence in the western and eastern Mediterranean through the Punic and Macedonian wars, but was then shaken by a century-long political crisis. Meanwhile, the popularity and wealth of Roman generals increased: notably Julius Caesar acquired fame for projecting military power north of the Alps into Gaul, east of the Rhine into Germania and across the English channel into Britain.