Mao was born on December 26, 1893, in Shaoshan, Hunan Province, China. His father was a poor peasant who had become a wealthy farmer and grain dealer. At age 8 he began studying at the village primary school, but left school at 13 to work on the family farm. He later left the farm to continue his studies at a secondary school in Changsha, the capital of Hunan province. When the Xinhai Revolution against the Qing Dynasty broke out in 1911 he joined the Revolutionary Army in Hunan. In the spring of 1912 the war ended, the Republic of China was founded and Mao left the army. He eventually returned to school, and in 1918 graduated from the First Provincial Normal School of Hunan.

Following his graduation, it is believed that Mao traveled with Professor Yang Changji, his college teacher and future father-in-law, to Beijing in 1919. Prior to his death in 1920, Professor Yang held a faculty position at Peking University, and at his recommendation, Mao worked as an assistant librarian at the University Library under the curatorship of Li Dazhao, who would come to greatly influence Mao's future thought. Mao registered as a part-time student at Beijing University and attended a few lectures and seminars by intellectuals, such as Chen Duxiu, Hu Shi, and Qian Xuantong. During his stay in Shanghai, he engaged himself as much as possible in reading which introduced him to Communist theories.

He married Yang Kaihui, Professor Yang's daughter and a fellow student, despite an existing marriage with Luo Yixiu arranged by his father at home, which Mao never acknowledged. In October 1930, the Kuomintang (KMT) captured Yang Kaihui as well as her son, Anying. The KMT imprisoned them both, and Anying was later sent to his relatives after the KMT killed his mother. At this time, Mao was living with He Zizhen, a co-worker and 17 year old girl from Yongxing, Jiangxi. Likely due to poor language skills (Mao never learned to speak Mandarin, having lived in a Xiang-speaking community), he turned down an opportunity to study in France.

On July 23, 1921, Mao, age 27, attended the first session of the National Congress of the Communist Party of China in Shanghai. Two years later, he was elected as one of the five commissars of the Central Committee of the Party during the third Congress session. Later that year, Mao returned to Hunan at the instruction of the CPC Central Committee and the Kuomintang Central Committee to organize the Hunan branch of the Kuomintang. In 1924, he was a delegate to the first National Conference of the Kuomintang, where he was elected an Alternate Executive of the Central Committee. In 1924, he became an Executive of the Shanghai branch of the Kuomintang and Secretary of the Organization Department.

For a while, Mao remained in Shanghai, an important city that the CPC emphasized for the Revolution. However, the Party encountered major difficulties organizing labor union movements and building a relationship with its nationalist ally, the KMT. The Party had become poor, and Mao became disillusioned with the revolution and moved back to Shaoshan. During his stay at home, Mao's interest in the revolution was rekindled after hearing of the 1925 uprisings in Shanghai and Guangzhou. His political ambitions returned, and he then went to Guangdong, the base of the Kuomintang, to take part in the preparations for the second session of the National Congress of Kuomintang. In October 1925, Mao became acting Propaganda Director of the Kuomintang.

In early 1927, Mao returned to Hunan where, in an urgent meeting held by the Communist Party, he made a report based on his investigations of the peasant uprisings in the wake of the Northern Expedition. His "Report on the Peasant Movement in Hunan" is considered the initial and decisive step towards the successful application of Mao's revolutionary theories.

After graduating from Hunan Normal School, the highest level of schooling available in his province, Mao spent six months studying independently. Mao was first introduced to communism while working at Peking University, and in 1921 he attended the organizational meeting of the Communist Party of China (or CPC). He first encountered Marxism while he worked as a library assistant at Peking University.

Other important influences on Mao were the Russian revolution and, according to some scholars, the Chinese literary works: Outlaws of the Marsh and Romance of the Three Kingdoms. Mao sought to subvert the alliance of imperialism and feudalism in China. He thought the KMT to be both economically and politically vulnerable and thus that the revolution could not be steered by Nationalists.

Throughout the 1920s, Mao led several labour struggles based upon his studies of the propagation and organization of the contemporary labour movements. However, these struggles were successfully subdued by the government, and Mao fled from Changsha, Hunan after he was labeled a radical activist. He pondered these failures and finally realized that industrial workers were unable to lead the revolution because they made up only a small portion of China's population, and unarmed labour struggles could not resolve the problems of imperial and feudal suppression.

Mao began to depend on Chinese peasants who later became staunch supporters of his theory of violent revolution. This dependence on the rural rather than the urban proletariat to instigate violent revolution distinguished Mao from his predecessors and contemporaries. Mao himself was from a peasant family, and thus he cultivated his reputation among the farmers and peasants and introduced them to Marxism.

His two 1937 essays, 'On Contradiction' and 'On Practice', are concerned with the practical strategies of a revolutionary movement and stress the importance of practical, grass-roots knowledge, obtained through experience.

Both essays reflect the guerilla roots of Maoism in the need to build up support in the countryside against a Japanese occupying force and emphasise the need to win over hearts and minds through 'education'. The essays, excerpts of which appear in the 'Quotations from Chairman Mao Zedong', warn against the behaviour of the blindfolded man trying to catch sparrows, and the 'Imperial envoy' descending from his carriage to 'spout opinions' .

In 1927, Mao conducted the famous Autumn Harvest Uprising in Changsha, as commander-in-chief. Mao led an army, called the "Revolutionary Army of Workers and Peasants", which was defeated and scattered after fierce battles. Afterwards, the exhausted troops were forced to leave Hunan for Sanwan, Jiangxi, where Mao re-organized the scattered soldiers, rearranging the military division into smaller regiments.

Mao also ordered that each company must have a party branch office with a commissar as its leader who would give political instructions based upon superior mandates. This military rearrangement in Sanwan, Jiangxi initiated the CPC's absolute control over its military force and has been considered to have the most fundamental and profound impact upon the Chinese revolution. Later, they moved to the Jinggang Mountains, Jiangxi.

In the Jinggang Mountains, Mao persuaded two local insurgent leaders to pledge their allegiance to him. There, Mao joined his army with that of Zhu De, creating the Workers' and Peasants' Red Army of China, Red Army in short. Mao's tactics were strongly based on that of the Spanish Guerillas during the Napoleonic Wars.

From 1931 to 1934, Mao helped establish the Soviet Republic of China and was elected Chairman of this small republic in the mountainous areas in Jiangxi. Here, Mao was married to He Zizhen. His previous wife, Yang Kaihui, had been arrested and executed in 1930, just three years after their departure.

It was alleged that Mao orchestrated the Anti-Bolshevik League incident and the Futian incident.

In Jiangxi, Mao's authoritative domination, especially that of the military force, was challenged by the Jiangxi branch of the CPC and military officers. Mao's opponents, among whom the most prominent was Li Wenlin, the founder of the CPC's branch and Red Army in Jiangxi, were against Mao's land policies and proposals to reform the local party branch and army leadership. Mao reacted first by accusing the opponents of opportunism and kulakism and then set off a series of systematic suppressions of them.

Under the direction of Mao, it is reported that horrible methods of torture took place and given names such as 'sitting in a sedan chair', 'airplane ride', 'toad-drinking water', and 'monkey pulling reins.' The wives of several suspects had their breasts cut open and their genitals burned. Short (2001) estimates that tens of thousands of suspected enemies, perhaps as many as 186,000, were killed during this purge. Critics accuse Mao's authority in Jiangxi of being secured and reassured through the revolutionary terrorism, or red terrorism.

Mao, with the help of Zhu De, built a modest but effective army, undertook experiments in rural reform and government, and provided refuge for Communists fleeing the rightist purges in the cities. Mao's methods are normally referred to as Guerrilla warfare; but he himself made a distinction between guerrilla warfare (youji zhan) and Mobile Warfare (yundong zhan).

Mao's Guerrilla Warfare and Mobile Warfare was based upon the fact of the poor armament and military training of the Red Army which consisted mainly of impoverished peasants, who, however, were all encouraged by revolutionary passions and aspiring after a communist utopia.

Around 1930, there had been more than ten regions, usually entitled "soviet areas", under control of the CPC. The relative prosperity of "soviet areas" startled and worried Chiang Kai-shek, chairman of the Kuomintang government, who waged five waves of besieging campaigns against the "central soviet area." More than one million Kuomintang soldiers were involved in these five campaigns, four of which were defeated by the Red Army led by Mao. By June 1932 (the height of its power), the Red Army had no less than 45,000 soldiers, with a further 200,000 local militia acting as a subsidiary force.

Under increasing pressure from the KMT encirclement campaigns, there was a struggle for power within the Communist leadership. Mao was removed from his important positions and replaced by individuals (including Zhou Enlai) who appeared loyal to the orthodox line advocated by Moscow and represented within the CPC by a group known as the 28 Bolsheviks.

Chiang, who had earlier assumed nominal control of China due in part to the Northern Expedition, was determined to eliminate the Communists. By October 1934, he had them surrounded, prompting them to engage in the "Long March", a retreat from Jiangxi in the southeast to Shaanxi in the northwest of China. It was during this 9,600 kilometer (5,965 mile), year-long journey that Mao emerged as the top Communist leader, aided by the Zunyi Conference and the defection of Zhou Enlai to Mao's side. At this Conference, Mao entered the Standing Committee of the Politburo of the Communist Party of China.

According to the standard Chinese Communist Party line, from his base in Yan'an, Mao led the Communist resistance against the Japanese in the Second Sino-Japanese War (1937—1945). However, Mao further consolidated power over the Communist Party in 1942 by launching the Shu Fan movement, or "Rectification" campaign against rival CPC members such as Wang Ming, Wang Shiwei, and Ding Ling. Also while in Yan'an, Mao divorced He Zizhen and married the actress Lan Ping, who would become known as Jiang Qing.

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During the Sino-Japanese War, Mao Zedong's military strategies, laid out in On Guerrilla Warfare were opposed by both Chiang Kai-shek and the United States. The US regarded Chiang as an important ally, able to help shorten the war by engaging the Japanese occupiers in China. Chiang, in contrast, sought to build the ROC army for the certain conflict with Mao's communist forces after the end of World War II. This fact was not understood well in the US, and precious lend-lease armaments continued to be allocated to the Kuomintang.

In turn, Mao spent part of the war (as to whether it was most or only a little is disputed) fighting the Kuomintang for control of certain parts of China. Both the Communists and Nationalists have been criticised for fighting amongst themselves rather than allying against the Japanese Imperial Army. Some argue, however, that the Nationalists were better equipped and fought more against Japan.

In 1944, the Americans sent a special diplomatic envoy, called the Dixie Mission, to the Communist Party of China. According to Edwin Moise, in Modern China: A History 2nd Edition:

Most of the Americans were favorably impressed. The CPC seemed less corrupt, more unified, and more vigorous in its resistance to Japan than the KMT. United States fliers shot down over North China...confirmed to their superiors that the CPC was both strong and popular over a broad area. In the end, the contacts with the USA developed with the CPC led to very little.

After the end of World War II, the U.S. continued to support Chiang Kai-shek, now openly against the People's Liberation Army led by Mao Zedong in the civil war for control of China. The U.S. support was part of its view to contain and defeat world communism. Likewise, the Soviet Union gave quasi-covert support to Mao (acting as a concerned neighbor more than a military ally, to avoid open conflict with the U.S.) and gave large supplies of arms to the Communist Party of China, although newer Chinese records indicate the Soviet "supplies" were not as large as previously believed, and consistently fell short of the promised amount of aid.

In 1948, the People’s Liberation Army starved out the Kuomintang forces occupying the city of Changchun. At least 160,000 civilians are believed to have perished during the siege, which lasted from June until October. PLA lieutenant colonel Zhang Zhenglu, who documented the siege in his book White Snow, Red Blood, compared it to Hiroshima: “The casualties were about the same. Hiroshima took nine seconds; Changchun took five months.”

On January 21, 1949, Kuomintang forces suffered massive losses against Mao's forces. In the early morning of December 10, 1949, PLA troops laid siege to Chengdu, the last KMT-occupied city in mainland China, and Chiang Kai-shek evacuated from the mainland to Taiwan (Formosa) that same day.