<P> The balance of power theory in international relations suggests that national security is enhanced when military capability is distributed so that no one state is strong enough to dominate all others . If one state becomes much stronger than others, the theory predicts that it will take advantage of its strength and attack weaker neighbors, thereby providing an incentive for those threatened to unite in a defensive coalition . Some realists maintain that this would be more stable as aggression would appear unattractive and would be averted if there was equilibrium of power between the rival coalitions . </P> <P> When confronted by a significant external threat, states that wish to form alliances may "balance" or "bandwagon". Balancing is defined as allying with others against the prevailing threat, while states that have bandwagoned have aligned with the threat . States may also employ other alliance tactics, such as buck - passing and chain - ganging . There is a longstanding debate among realists with regard to how the polarity of a system impacts on which tactic states use, however, it is generally agreed that bipolar systems as each great power has no choice but to directly confront the other . Along with debates between realists about the prevalence of balancing in alliance patterns, other schools of international relations, such as constructivists, are also critical of the balance of power theory, disputing core realist assumptions regarding the international system and the behavior of states . </P> <P> The principle involved in preserving the balance of power as a conscious goal of foreign policy, as David Hume pointed out in his Essay on the Balance of Power, is as old as history, and was used by Greeks such as Thucydides both as political theorists and as practical statesmen . </P> <P> It resurfaced in Renaissance among the Italian city - states in the 15th century . Francesco Sforza, Duke of Milan, and Lorenzo de' Medici, ruler of Florence, were the first rulers actively to pursue such a policy, with the Italic League, though historians have generally attributed the innovation to the Medici rulers of Florence . Discussion of the Florentine activity can be found in De Bello Italico, by Bernardo Rucellai, a Medici son - in - law . This was a history of the invasion of Italy by Charles VIII of France, and introduced the phrase balance of power to historical analysis . </P>

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