Alliance

When spelled with a capital "A", "the Allies" usually denotes the countries who fought together against the Central Powers in World War I (the Allies of World War I), or those who fought against the Axis Powers in World War II (the Allies of World War II).

In the second half of the 20th century, the Cold War was characterised by the intense rivalry between the military alliances of NATO and the Warsaw Pact, as each competed to expand and maintain their spheres of influence.

More recently, the term "Allied forces" has also been used to describe the coalition of the Gulf War, as opposed to forces the Multi-National Forces in Iraq which are commonly referred to as "Coalition forces" or, as by the George W. Bush administration, "the coalition of the willing".

At the onset of the 21st century, shifts in the global order led to the formation of new alliances rooted in ideological and historical precedents, exemplified by Brazil, Russia, India, China, and South Africa (BRICS). This alliance possesses a broad and vaguely defined agenda, with its members exhibiting varying degrees of commitment to and motivations for participating in this initiative. The inaugural BRICS meeting occurred in 2006. In 2023, the alliance expanded with the invitation of six new members, Argentina, Egypt, Ethiopia, Iran, Saudi Arabia, and the United Arab Emirates, and was rebranded as BRICS Plus.

Scholars are divided as to the impact of alliances. Several studies find that defensive alliances deter conflict. One study questions these findings, showing that alliance commitments deterred conflict in the prenuclear era but has no statistically meaningful impact on war in the postnuclear era. Another study finds that while alliance commitments deter conflict between sides with a recent history of conflict, alliances tend to provoke conflicts between states without such a history.

A 2000 study in the Journal of Conflict Resolution found that allies fulfill their alliance commitments approximately 75% of the time. Most research suggests that democracies are more reliable allies than non-democracies. A 2004 study did however question whether alliance commitments by democracies are more durable. A 2018 study updated and extended the data from the 2000 Journal of Conflict Resolution study and found that allies only fulfill their commitments about 50% of the time from 1816 to 2003. According to the study, "States honored their alliance commitments 66% of the time prior to 1945 but the compliance rate drops to 22% from 1945 to 2003. Moreover, the rates of fulfillment for defense pacts (41%) and nonaggression pacts (37%) are dramatically lower than offensive alliances (74%) and neutrality agreements (78%)."

One of the most profound effects of alliances can be seen in technological innovation, due to conduits of knowledge flows that are open between allies but closed between rivals.

According to a 2017 poll by WIN/GIA, the United States was the most preferred ally internationally. Russia, Iran, North Korea, and China (CRINK), who preferred one another, both trailed America globally. Four countries, Bulgaria, Greece, Slovenia and Turkey, preferred Russia, despite being members of NATO.

In Pakistan, 72% of respondents preferred ties to China, the largest margin of any country surveyed, while 46% of Bangladesh preferred India. A total of 22 countries indicated a preference for the United Kingdom at a rate of 10% or more, but the United States was the only country to prefer Britain over any other, at a rate of 43%. Five countries preferred France at a rate of 10% or more, led by Belgium at a rate of 25%. A single country, Iraq, expressed no preference, while three other countries, Lebanon, Palestine, and Slovenia, expressed no preference at a rate of 11% or more, although at a smaller rate than their preference for Russia on the part of Lebanon and Slovenia, and China on the part of Palestine. Kosovo reported the most unified opinion, preferring the United States at a rate of 92%, while Russia's most unified supporters were Mongolia (71%), Armenia (67%) and Serbia (56%). In total, 21 countries expressed a preference for America at a rate of 50% or more.