List of war crimes
Spanish mutilations of captured Moroccans were reported, including castration and severing heads, noses and ears, which were collected by Spanish legionnaries as war trophies and worn as necklaces or spiked on bayonets.
On August 9, 1921, the Massacre of Monte Arruit occurred, in which 2,000 soldiers of the Spanish Army were killed by Riffian forces after surrendering the Monte Arruit garrison near Al Aaroui following a 12-day siege.

1923–1932: Pacification of Libya: The Pacification of Libya resulted in mass deaths of the indigenous people in Cyrenaica by Italy. 80,000 or over a quarter of the indigenous people in Cyrenaica perished during the pacification.
100,000 Bedouin citizens were ethnically cleansed by expulsion from their land.
Specific war crimes alleged to have been committed by the Italian armed forces against civilians include deliberate bombing of civilians, killing unarmed children, women, and the elderly, rape and disembowelment of women, throwing prisoners out of aircraft to their death and running over others with tanks, regular daily executions of civilians in some areas, and bombing tribal villages with mustard gas bombs beginning in 1930.

1927-1949: Chinese Civil War: During the Chinese Civil War both the Nationalists and Communists carried out mass atrocities, with millions of non-combatants deliberately killed by both sides. Benjamin Valentino has estimated atrocities in the Chinese Civil War resulted in the death of between 1.8 million and 3.5 million people between 1927 and 1949.
Over several years after the 1927 Shanghai massacre, the Kuomintang killed between 300,000 and one million people, primarily peasants, in anti-communist campaigns as part of the White Terror. During the White Terror, the Nationalists specifically targeted women with short hair who had not been subjected to foot binding, on the presumption that such "non-traditional" women were radicals. Nationalist forces cut off their breasts, shaved their heads, and displayed their mutilated bodies to intimidate the populace. From 1946 to 1949, the Nationalists arrested, tortured, and killed political dissidents via the Sino-American Cooperative Organization.
During the December 1930 Futian incident, the communists executed 2,000 to 3,000 members of the Futian battalion after its leaders had mutinied against Mao Zedong. Between 1931 and 1934 in the Jiangxi–Fujian Soviet, the communist authorities engaged in a widespread campaign of violence against civilians to ensure compliance with its policies and to stop defection to the advancing KMT, including mass executions, land confiscation and forced labor. According to Li Weihan, a high-ranking communist in Jiangxi at the time, in response to mass flight of civilians to KMT held areas, the local authorities authorities would "usually to send armed squads after those attempting to flee and kill them on the spot, producing numerous mass graves throughout the CSR [Chinese Soviet Republic in Jiangxi] that would later be uncovered by the KMT and its allies." Zhang Wentian, another high-ranking communist, reported that "the policy of annihilating landlords as an exploiting class had degenerated into a massacre" The population of the communist controlled area fell by 700,000 from 1931 and 1935, of which a large proportion were murdered as “class enemies,” worked to death, committed suicide, or died in other circumstances attributable to the communists.
During the Siege of Changchun the People's Liberation Army implemented a military blockade on the KMT-held city of Changchun and prevented civilians from leaving the city during the blockade; this blockade caused the starvation of tens to 150 thousand civilians. The PLA continued to use siege tactics throughout Northeast China.
At the outbreak of the Chinese Civil War in 1946, Mao Zedong began to push for a return to radical policies to mobilize China against the landlord class, but protected the rights of middle peasants and specified that rich peasants were not landlords. The 7 July Directive of 1946 set off eighteen months of fierce conflict in which all rich peasant and landlord property of all types was to be confiscated and redistributed to poor peasants. Party work teams went quickly from village to village and divided the population into landlords, rich, middle, poor, and landless peasants. Because the work teams did not involve villagers in the process, however, rich and middle peasants quickly returned to power. The Outline Land Law of October 1947 increased the pressure. Those condemned as landlords were buried alive, dismembered, strangled and shot.
In response to the aforementioned land reform campaign; the Kuomintang helped establish the "Huanxiang Tuan" (還鄉團), or Homecoming Legion, which was composed of landlords who sought the return of their redistributed land and property from peasants and CCP guerrillas, as well as forcibly conscripted peasants and communist POWs. The Homecoming legion conducted its guerrilla warfare campaign against CCP forces and purported collaborators up until the end of the civil war in 1949.

1935–1937: Second Italo-Abyssinian War: Italian use of mustard gas against Ethiopian soldiers in 1936 violated the 1925 Geneva Protocol, which bans the use of chemical weapons in warfare.
Crimes by Ethiopian troops included the use of dum-dum bullets (in violation of the Hague Conventions), the killing of civilian workmen (including during the Gondrand massacre), and the mutilation of captured Eritrean Ascari and Italians (often with castration), beginning in the first weeks of war.
Yekatit 12—In response to the unsuccessful assassination of Rodolfo Graziani on 19 February 1937, thousands of Ethiopians were killed, including all of the monks residing at Debre Libanos, and over a thousand more detained at Danan who were then exiled either to the Dahlak Islands or Italy.
The Ethiopians recorded 275,000 combatants killed in action, 78,500 patriots (guerrilla fighters) killed during the occupation, 17,800 civilians killed by aerial bombardment and 30,000 in the February 1937 massacre, 35,000 people died in concentration camps, 24,000 patriots executed by Summary Courts, 300,000 people died of privation due to the destruction of their villages, amounting to 760,300 deaths.

1936–1939: Spanish Civil War: At least 50,000 people were executed during the Spanish Civil War. In his updated history of the Spanish Civil War, Antony Beevor writes, "Franco's ensuing 'white terror' claimed 200,000 lives. The 'red terror' had already killed 38,000." Julius Ruiz concludes that "although the figures remain disputed, a minimum of 37,843 executions were carried out in the Republican zone with a maximum of 150,000 executions (including 50,000 after the war) in Nationalist Spain."
César Vidal puts the number of Republican victims at 110,965. In 2008 a Spanish judge, Baltasar Garzón, opened an investigation into the executions and disappearances of 114,266 people between 17 July 1936 and December 1951. Among the murders and executions investigated was that of poet and dramatist Federico García Lorca.

1939–1945: World War II: 

1946–1954: Indochina War: The French Union's struggle against the independence movement backed by the Soviet Union and China claimed 400,000 to 1.5 million Vietnamese lives from 1945 to 1954. In the Haiphong massacre of November 1946, about 6,000 Vietnamese were killed by French naval artillery. The French employed electric shock treatment during interrogations of the Vietnamese, and nearly 10,000 Vietnamese perished in French concentration camps.
According to Arthur J. Dommen, the Viet Minh assassinated 100,000–150,000 civilians during the war, while Benjamin Valentino estimates that the French were responsible for 60,000 to 250,000 civilian deaths.
About French massacres and war crimes during the conflict, Christopher Goscha wrote on The Penguin History of Modern Vietnam: "Rape became a disturbing weapon used by the Expeditionary Corps, as did summary executions. Young Vietnamese women who could not escape approaching enemy patrols smeared themselves with any stinking thing they could find, including human excrement. Decapitated heads were raised on sticks, bodies were gruesomely disemboweled, and body parts were taken as 'souvenirs'; Vietnamese soldiers of all political colors also committed such acts. The non-communist nationalist singer, Phạm Duy, wrote a bone-chilling ballad about the mothers of Gio Linh village in central Vietnam, each of whom had lost a son to a French Army massacre in 1948. Troops decapitated their bodies and displayed their heads along a public road to strike fear into those tempted to accept the Democratic Republic of Vietnam's sovereignty. Massacres did not start with the Americans in My Lai, or the Vietnamese communists in Hue in 1968. And yet, the French Union's massacre of over two hundred Vietnamese women and children in My Tratch in 1948 remains virtually unknown in France to this day."