Perpetual war
Causes: Poor military planning is one of the major reasons that a forever war can occur. If the territory gained in a war is not occupied or controlled properly, this can allow a deadly insurgency to occur, potentially stretching out a conflict that never ends. Similarly, warfare that is fought irregularly, such as rebellions in Africa, do not have a set of military objectives in mind, usually because these rebel groups intend to commit war crimes against the civilian population. Thus, the lack of actual military goals can in itself be a reason that a forever war can occur.  A very large defense budget may also be a factor in the transpiration of a forever war. As of 2018, the United States has an inflation-adjusted military budget that is greater than its budget for World War II, which enables it to fight continuously in Iraq and other countries.
Civil wars are prone to military stalemate which can prolong the war indefinitely. A lack of democracy is associated with an increased risk of civil war.
Forever wars can occur in order to keep money flowing into institutions, such as the military–industrial–congressional complex (MICC). Thus, forever wars can serve as domestic political engines, as policy makers promote policies of continuing and expanding wars.
Forever wars can be to the benefit of small armed groups, who may achieve political goals by wearing down a larger group or country. For example, in the aftermath of the 9/11 attacks and the beginning of the war on terror, Al-Qaeda aimed to involve the United States in a prolonged guerrilla war in Afghanistan, challenging its will to fight such a long war.
Wars between ethnic or ideological groups can become forever wars, as such wars are harder to end with a negotiated peace deal due to the different interests of the two sides. An additional barrier may arise in the case of religious wars if one or both parties believe that the other must be destroyed.

In current events: The concept of a perpetual war has been used since opposition to United States involvement in the Vietnam War. James Pinckney Harrison argues in The Endless War: Fifty Years of Struggle in Vietnam (1981) that the Vietnam War was "endless" due to the success of the communist revolution in nationalizing the people. The concept was used by Trần Văn Đôn, a general in the Army of the Republic of Vietnam, in his book Our Endless War: Inside Vietnam (1978).
American historian James Chace argues in his book Endless War: How we got involved in Central America (1983) that US policy in Central America is based upon the assumption that US hegemony is threatened within the region. According to Chace, US involvement in Central America worked towards resisting the domino effect of the spread of a "communist take-over", largely through establishing the credibility of US military. Though these policies were meant to deter conflict, they themselves created the conditions for instability in the region, which furthered a US response. This resulted in a self-perpetuating, or "endless", loop. He additionally argues US investment in pursuing an expanding military presence in Central America reflects an endless preparation for war.
A key argument of Chace is that much of this military involvement stems from a logic of US paranoia in reaction to the Cuban Revolution. A similar argument is put forward by David Keen, political economist and Professor of Complex Emergencies at the London School of Economics. His book Endless War? Hidden Function of the 'War on Terror' (2006) argues that the United States' strategies and tactics in the war on terror use a "militaristic state-cased framework". This framework, though "counterproductive", has an "inner logic" and a "psychological function" of responding to the trauma of September 11 attacks.
Noam Chomsky posits that a state of perpetual war is an aid to (and is promoted by) the powerful members of dominant political and economic classes, helping maintain their positions of economic and political superiority.
British journalist Robert Fisk, a critic of Western policies in the Middle East, argues that recent Western conflicts against the Middle East, after the end of the Cold War, have been part of a new perpetual war. He suggests that former U.S. President George H. W. Bush launched attacks on Iraq, Sudan, and Afghanistan to distract the population from his domestic political problems. In addition, he claims that despite victorious claims after the first Gulf War that Saddam Hussein had been "defanged", he was again the target of Western attacks until his execution in 2006.
Similarly, Ted Koppel described the war on terror as "Our Children's Children's War". Critics of Western policies have used the term "perpetual war" in reference to non-military "wars", such as the "War on Drugs", "War on Poverty", "War on Cancer", Lou Dobbs's "War on the Middle Class", the "War on Terrorism", the "War on Women", or Bill O'Reilly's "War on Christmas".

In socioeconomics and politics: The economic make-up of the 5th century BC Athens-led Delian League also bears resemblance to the economic ramifications of preparing for perpetual war.  Aspects of any given empire, such as the British Empire and its relation to its domestic businesses that were owned by a wealthy minority of individuals, such as the East India Company, the Hudson's Bay Company, and De Beers, manifest an observed relationship between a minority of individuals influencing Empire or State policy, such as the Child's War in India, the Anglo-Mysore Wars in India, the Anglo-French conflicts on Hudson Bay in Canada, and the Second Boer War in South Africa, follow a pattern where the Empire allocates resources pursuing and sustaining policies that financially profit the Empire's domestic business's owners.

Military–industrial complex: The concept of a military–industrial complex was first suggested by U.S. President Dwight D. Eisenhower and the idea that military action can be seen as a form of market-creation goes back at least as far as speeches beginning in 1930 prior to the publication of War Is a Racket in 1935. On January 16, 1961, President Eisenhower delivered his farewell speech expressing great concern for the direction of the newfound armaments industry post-WWII. While recognizing the boom in economic growth after the war, he reminded the people of United States that this was a way of profiting off warfare and that if not regulated enough it could lead to the "grave" expansion of the armaments industry. For his warning of the thirst to profit from warfare through weapon production, Eisenhower coined the term "military industrial complex". He said, "The potential for the disastrous rise of misplaced power exists and will persist." Eisenhower feared that the military–industrial complex could lead to a state of perpetual war as the big armament industry will continue to profit from warfare. Additionally, NSC 68 can be used as a reference to understand U.S. President Harry S. Truman's reasoning for the continued build up the United States' nuclear arsenal and how this contributed to the Cold War. This concept is still present in today's policies as William D. Hartung states in his article "The Doctrine of Armed Exceptionalism".

War on terror: Traditionally, the term "war" referred to the physical and conventional act of engaging in armed conflict. However, the implications of what war entails has evolved over time. The war on terror has often been cited as a perpetual war, being a war with "no specific battlefield and the enemy isn’t an army." The war on terror has been directed at countless "enemies," as it has no clear target. Georgetown University Historian Bruce Hoffman describes traditional war as a war that "ends with the vanquishing of an opponent, with some form or armistice or truce- some kind of surrender instrument or document." In contrast, the war on terror continues with no end in sight.
The war on terror was declared in 2001 by President George W. Bush, following the September 11 attacks, but as early as 1996, Osama bin Laden of Al-Qaeda made a threat to the United States, by making a declaration of war. The growing tensions of the Middle East are suggested by Laurence Andrew Dobrot to be very wide cultural misunderstandings and faults the West for not making peace with the Middle East. As the deputy director for the Missile Defense Agency's Airborne Laser Program, Dobrot examines the hostility which has been continuous not only since 2001, but since the birth of Wahhabism.
Dobrot proposed that the U.S should recognize the cultural hostility of the tribal Arabs in order to make the first steps towards progression of making peace.
The Crusades arose as European expansion was growing at the peak of unified Islamic dominance. On September 16, 2001, in a speech, President Bush referred to the war on terror as a crusade. He said:

 No one could have conceivably imagined suicide bombers burrowing into our society and then emerging all in the same day to fly their aircraft - fly U.S. aircraft into buildings full of innocent people - and show no remorse.  This is a new kind of  -- a new kind of evil.  And we understand.  And the American people are beginning to understand.  This crusade, this war on terrorism is going to take a while.  And the American people must be patient.  I'm going to be patient.
Andrew Bacevich described Bush's naming of the war on terror as a crusade as something which does not make the war separate, rather something that shows that it is part of an "eternal war."