Unilateralism is an antonym for multilateralism. The two terms can refer to differences in approach to international problems. When agreement by multiple parties is absolutely required, such as aviation policies, bilateral agreements (involving two participants at a time) are usually preferred by proponents of unilateralism.

Unilateralism may be preferred in those instances when it's assumed to be the most efficient, i.e. in issues that can be solved without cooperation. However, a government may also have a principal preference for unilateralism or multilateralism, and for instance strive to avoid policies that can't be realized unilaterally, alternatively to champion multilateral solution also to problems that seen isolated equally well could have been solved unilaterally.

Typically, governments may argue that their ultimate or middle-term goals are served by a strengthening of multilateral schemes and institutions, as was many times the case during the period of the Concert of Europe.

U.S. unilateralism debate

Unilaterlism is today generally associated with the War in Iraq. While over 30 countries have supported the U.S. policy, traditionally close American allies, for instance France, Germany and Turkey, are not participating. Many others are very outspoken, giving light to the perception that America is "going alone" in Iraq without the support of multilateral institutions - in this case NATO and the UN, which America has relied on in the world order established after World War II.

One argument advocating unilaterlism is that other countries should not have "veto power" over matters of U.S. National Security. Presidential Candidate John Kerry received heavy political heat after a statement during the Presidential Debates that in order to move to protect America, its actions must pass a "global test". This was interpreted by his opponents as granting "veto power" to currently-unpopular countries, such as France and Germany, or long-time foes such as Russia, similar to the often exercised U.S. veto in the United Nations Security Council.

Critics of American unilateralism point to the ethical implications of engaging in armed conflicts that may inevitably draw in combatants from other nations, as well as the undermining of the international ability to protect small nations from aggressors. Unilateralism can be considered nothing more than a positively-sold version of the very actions that would earn other states the title of rogue nations. Unilateralism rejects the essential interwoven nature of modern global politics and perhaps underestimates the extent to which a conflict in one country can affect civilians in others. This raises the ethical dilemma of forcing involvement from peoples who have voted in anti-war governments, or whose nations refused to show support for the US actions or strategies involved.

Multilateralism, on the other hand, would provide a country with greater resources, both militarily and economically, and would help in defraying the cost of military action. However, with divided responsibility inevitably comes divided authority, and thus (in theory at least) slower military reaction times and the demand that troops follow commanders from other nations.

Multilaterlists argue that co-operations strengthens the bonds between nations and peoples, paints the US in a more responsible and respected light, and reduces the risk of wildfire conflicts by increasing the size and unity of the enemy such a rogue nation would face.