Democratic Peace Theory is the most historically verifiable international relations theory and contributes to global stability

It was not, however, until World War I that the full democratic peace proposition became central to foreign policy. Wilson's war message in April 1917 -- in which he declared that the battle between autocracies and democracies would establish "the principles of peace and justice" -- was the clarion call. The clash between democracy and autocracy continued to shape policy as the decades went on. The behavior of the United States during the Cold War, for example, was often motivated by a belief that spreading liberal values would yield peace. As Secretary of State John Foster Dulles declared in his 1953 Senate confirmation hearing, "We shall never have a secure peace or a happy world so long as Soviet communism dominates one-third of all the peoples that there are." President John F. Kennedy echoed that theme in his 1963 speech in West Berlin, declaring that "when all are free, then we can look forward to that day when this city will be joined as one and this country and this great Continent of Europe in a peaceful and hopeful globe." But that same month, in a powerful address at American University, Kennedy warned of the complementary dangers of ideological confrontation with the Soviet Union. "Let us not be blind to our differences -- but let us also direct attention to our common interests and the means by which those differences can be resolved," he said. "If we cannot end now our differences, at least we can help make the world safe for diversity."TIME AFTER TIME As liberalism endured and spread, intellectuals began empirically testing whether democratic peace theory actually held true. In 1939, the American journalist Clarence Streit published a qualitative historical analysis to see whether liberal democracies tended to maintain peace among themselves. Discerning that the answer was yes, he proposed that the decade's leading democracies form a federal union, which would help protect them from fascist powers. In 1972, Dean Babst, building on Quincy Wright's magisterial^ Study of War from 30 years earlier, carried out a statistical analysis that also suggested a correlation between democracy and peace. In 1976, Melvin Small and J. David Singer confirmed this finding but demonstrated that democratic peace was limited to relations between democracies. Republics, they showed, were still prone to fight autocratic regimes. In the decades since, international relations scholars have continued to study the democratic peace paradigm. They have shown that the relationship between democracy and peace is statistically significant even when controlling for proximity, wealth, and trade. They have determined that the theory holds even when states attempt to constrain each other. Academics have advanced a wide variety of explanations for why the concept is so sturdy. Some have argued that part of the reason lies in the disproportionate influence that international institutions have with liberal countries. Research shows that democracies tend to delegate a lot of policymaking to complex multilateral bodies, such as the European Union and the World Trade Organization, in part because their leaders can use these groups to entrench policies before cycling out of office. Other scholars have argued that liberal norms favoring peace, human rights, and respect for fellow democracies hold sway over policymakers and publics. And still others have pointed to the benefits of trade and economic interdependence associated with relations among capitalist democracies. States that frequently trade, after all, will lose wealth if they fight one another. Still, democratic peace theory has attracted plenty of critics. Henry Farber and Joanne Gowa have pointed out that there are other forces at work in stopping wars between democracies. During the Cold War, for example, NATO'S need to protect itself from the Soviet bloc ensured that Western Europe cooperated -- although the region's post-Cold War peace suggests more than collaborative containment is at work. Other scholars have pointed out that none of the factors used to explain democratic peace theory can stop war on its own. States that are deeply involved in international institutions, after all, do launch invasions. Peaceful norms and ideas work only if democracies heed them in the policymaking process, yet they are often ignored. The shared decision-making powers of republics should encourage deliberation, but the division of powers and rotation of elites can also lead democracies to send mixed signals, putting other states on edge. And economic benefits can be achieved through plunder, not just through trade. Powerful democratic states can have rational incentives to exploit wealthy, weak democracies, especially if the latter are endowed with natural resources or strategic assets such as shipping lanes. Rational material interest is not enough to explain why xenophobic democracies have not tried to conquer democracies of other ethnic groups. But put all the explanatory factors together, and democratic peace theory coheres. When governments are constrained by international institutions, when political elites or the electorate are committed to norms of liberty, when the public's views are reflected through representative institutions, and when democracies trade and invest in one another, conflicts among republics are peacefully resolved.