Attrition warfare
Strategic considerations: Attrition warfare represents an attempt to grind down an opponent's ability to make war by destroying their military resources by any means including guerrilla warfare, people's war, scorched earth and all types of battles apart from a decisive battle. Attrition warfare does not include Blitzkrieg or using concentration of force and a decisive battle to win. The side that reinforces their army at a higher speed will normally win the war. Clausewitz called it the exhaustion of the adversary.
A side that perceives itself to be at a marked disadvantage may deliberately seek out attrition warfare to neutralize its opponent's advantages over time. Sun Tzu has stated that there is no country that has benefitted from prolonged warfare, but Russia in 1812 won the war with attrition warfare against Napoleon. When attritional methods have worn down the enemy sufficiently to make other methods feasible, attritional methods are often complemented or even abandoned by other strategies. World War I military commanders on both sides ineffectively relied on attrition warfare, which resulted in casualties without a strategic result.
The difference between war of attrition and other forms of war is somewhat artificial since even a single battle normally contains an element of attrition. A strategy of attrition is pursued when the primary objective is to gradually weaken the opponent to a point of unacceptable or unsustainable loss, while simultaneously ensuring that one's own losses remain within acceptable and sustainable limits. That should be seen as opposed to other main goals such as the conquest of some resource or territory or an attempt to cause the enemy great losses in a single stroke (such as by encirclement and capture). Attrition warfare also tries to increase the friction in a war for the opponent.
While attrition warfare might appear to be a strategic option for combatants possessing greater resources or asymmetric advantages over their adversaries, it also carries considerable drawbacks. Perhaps the most common reason for failure of attrition warfare is related to the time required to fulfill one's war goals. The geopolitical and strategic situation may shift dramatically over long periods of time, potentially giving the opponent an edge if victory is not achieved soon enough. Additionally, the attrition strategies gives opponents time to adjust tactics and strategy. Although the strategy is typically victorious for the more well-resourced nation, it may eventually fail due to operational and geopolitical mishaps, such as Athens during the Peloponnesian War, or due to strategic miscalculations, such as Germany during the Battle of Britain.

Examples in history: 

Most typical: The French invasion of Russia is a textbook example of attrition warfare, where Russia interfered with Napoleon's military logistics and won the war without a decisive battle. One of the best visual representations of the Russian attrition warfare strategies was created by Charles Joseph Minard. It shows the steady decrease of the number of soldiers of the French Grande Armée during the course of the war.

Best known: One commonly known example of attrition warfare might be on the Western Front during World War I. Both military forces found themselves in static defensive positions in trenches running from Switzerland to the English Channel. For years, without any opportunity for maneuvers, the only way the commanders thought that they could defeat the enemy was to repeatedly attack head on and grind the other down.
One of the most enduring examples of attrition warfare on the Western Front is the Battle of Verdun, which took place throughout most of 1916. Erich von Falkenhayn later claimed that his tactics at Verdun were designed not to take the city but rather to destroy the French Army in its defense. Falkenhayn is described as wanting to "bleed France white" and thus the attrition tactics were employed in the battle.
Soldiers on the Italian Front fought a series of battles of attrition along the Isonzo River between June 1915 and November 1917.

Attritional warfare in World War I has been shown by historians such as Hew Strachan to have been used as a post hoc ergo propter hoc excuse for failed offensives. Contemporary sources disagree with Strachan's view on this. While the Christmas Memorandum is a post-war invention, the strategy of attritional warfare was the original strategy for the battle.

List of wars: Scythian tactics during the European Scythian campaign of Darius I of 513 BC, which was in deep steppes retreat, avoiding a direct confrontation with Darius I's army, while spoiling the wells and pastures.
The Athenians, who were weaker in land warfare during the Peloponnesian War, employed attrition warfare using their navy.
The "delaying" tactics of Quintus Fabius Maximus Verrucosus (surnamed "Cunctator", the delayer) against Hannibal during the Second Punic War.
Muhammad Tapar's campaign against the Nizaris of Alamut in 1109–1118
Second Mongol invasion of Hungary in 1285 and 1286
Fall of Tenochtitlan by Hernán Cortés in 1521
Swedish invasion of Russia in 1708
The American strategy during the American Revolutionary War
The latter portion of the American Civil War, notably the siege of Vicksburg, the overland campaign, and the siege of Petersburg
The Attrition warfare against Napoleon in the French invasion of Russia by Napoleon Bonaparte in 1812
The later battles of the Philippine–American War
The latter stages of the Spanish Civil War (1938–1939)
The Chinese strategy during the Second Sino-Japanese War
Tonnage war in the Atlantic and Pacific during World War II
The Air battle for Great Britain in World War II after the bombing of London
Static battles in World War II, including Soviet urban defense during the Battle of Stalingrad
Battle of Tabu-dong, and the final two years of the Korean War
The Vietnam War
The "Long War" during the Provisional IRA's armed campaign against the British Army during the Troubles.
The Israeli–Egyptian War of Attrition from 1967 to 1970.
The Soviet–Afghan War and later the Afghan Civil War (1989–1992)
The later phases of the Iran–Iraq War
The Yugoslav Wars (1991–2001): especially the Bosnian War (1992–1995), the Croatian War (1991–1992 and 1995), and the Kosovo War (1998–1999).
The War in Afghanistan (2001–2021)
The Sri Lankan Civil War after 2005
The 2011 Libyan civil war
Kurdish–Turkish conflict (1978–present)
The Syrian civil war (2011–present), in particular the Battle of Aleppo (2012–2016).
The fight of the Polisario Front in Western Sahara against the Moroccan Army (2020–present).
The Tigray War between the Ethiopian government and Tigray rebels (2020–2022).
During the 2022 Russian invasion of Ukraine, the Russian military adopted a strategy of attrition.
The Israel–Hamas war (2023–present)

See also: Asymmetric warfare
Demoralization (warfare)
Guerrilla warfare
Human wave attack
Mexican standoff
No-win situation
Pyrrhic victory
Winner's curse
Win-win game

Military theory: Fabian strategy
Flypaper theory (strategy)
Ivan Bloch
Lanchester's laws
Loss Exchange Ratio
Maneuver warfare
New generation warfare

Notes: 

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nctimes (2012). "Airstrikes turn Libya conflict into battle of attrition". Archived from the original on 4 September 2012. Retrieved 3 April 2021.{{cite web}}:  CS1 maint: bot: original URL status unknown (link)
Sun Tzu (2004). The Art of War. Retrieved 3 April 2021.