Alright, next update is Korea, I promise! I just felt like throwing more oil on the fire of feverish Southeast Asia speculation.
The Burma War
Under the Maoist theory of war, revolutionary movements need to capture the periphery rural areas, build them into a revolutionary base area, and then drive into the core center from there. This tactic largely succeeded in Northeast China, and Mao intended to continue his application of this theory. However, the central country (Republican China) had largely not fallen yet. As a result, Maoist theory meant working towards a final confrontation by building more revolutionary base areas around the ROC - surrounding it with other Communist states.
As a result, Mao Zedong assumed control of the Second Field Army of the People’s Liberation Army, and instead of heading north, drove the army south, straight across the Yunnan-Burma border[1], to lend his support to the Communist insurgency against the Burmese military government. The People's Republic of China immediately denied all involvement or knowledge of Mao's plans, but few believed them except the Soviet Union, which had actual knowledge that Mao did not inform them of his plans. Most in the USSR were horrified at this provocation, but Stalin approved of Mao's plan after-the-fact.[2]
Mao had considered plunging into Vietnam, but he considered the internal politics too dicey and the nationalism too threatening, having heard of the various purges and counter-purges between the Vietnamese Communists of Ho Chi Minh and the Vietnamese Nationalists. However, Burma had a remarkably multifaceted rebellion against the government. With the Communist Party of Burma (“Red Flags”) and various ethnic movements in revolt, Mao figured he could build a Revolutionary Base Area in Burma as one of many groups. The Red Flags referred to the members of the Communist Party of Burma under Than Tun who refused to join in a coalition with the ruling Anti-Fascist People's Freedom League of U Nu, something done by the Communist Party of Burma "White Flags." Although the Red Flags started out the smaller dissident group in 1946, by the time Mao arrived in 1948, they had become the overwhelmingly larger group due to the AFPFL's marginalization of the White Flags.
Surprisingly, Mao was most popular not with Burma’s Chinese community, but rather with anti-government groups who viewed Mao’s “Yellow Flag Communists” as more or less a neutral arbiter on most ethnic issues. The quick acceptance of Mao’s aid surprised most international observers, but Burmese Communists believed his insistence that he had no imperial ambitions in Burma (due to his home country being across thousands of miles of his archenemy).[2]
In addition, Mao was one of the most enthusiastically violent proponents of land reform, with his Yellow Flags engaging in mass violence against landlords and suspected “class traitors,” a category of people that ended up significantly far larger than anyone could reasonably believe existed in a agrarian society. Finally, Mao’s army clearly outstripped both their allies and enemies in both military and administrative experience. With these advantages, the three Communist parties quickly coalesced into the “Popular Front for the Liberation of Burma,” with Mao as the theoretical weakest, but de facto strongest leader.
In response to the worrying advance of the Communists in Burma, British foreign affairs encouraged the overthrow of Prime Minister U Nu in a coup, bringing to power the more military-orientated Ne Win who British special forces concluded could defeat Mao. However, Ne Win proved to be a considerably more disastrous leader, unleashing waves of ethnic repression and bizarre economic policies that drove more peasants into the hands of the Communist front.[3] Worst of all, the socialist Ne Win’s vicious persecution of Chinese and Indian Burmese merchants alienated both Chiang and Nehru, who condemned Mao and forged closer ties with the UK, but did nothing to help Ne Win.[4] His troops would also engage in a terror spree in the countryside, hoping to massacre enough villages (especially ethnic minorities) in gruesome spectacles until there would be no more left capable of supplying Communist insurgents. Many members of the White Flag Communists were summarily executed by Ne Win's death squads after it was shown that many of them were supplying intelligence to the Red Flag Communists, causing the survivors to flee into the hands of the Red Flags.
As the situation continued to deteriorate, Prime Minister Churchill declared that Mao’s intervention in Burma constituted an invasion of Burma by Communist China, and in 1950, the first British, Canadian, Australian, and New Zealander forces landed in Burma, only 2 years after Burma’s hard-won independence.[5]
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[1] OTL, after the Civil War, a KMT army crossed that same border and camped out in Burma fighting with the Burmese government, but Mao comes with a LOT more men than the KMT ever did - and he's actively trying to forge a pan-Communist coalition to take down the central government.
[2] Mirrors OTL Stalin sorta-passively green-lighting the North Korea invasion of South Korea.
[3] OTL Ne Win literally declared all cash illegitimate and established a new base-9 currency because an astrologist told him 9 was a lucky number. Needless to say, the OTL Ne Win regime was known for total economic collapse. I'm pretty sure even Maoist China had a better record on economic growth than Ne Win's regime.
[4] Chiang doesn't take Mao seriously, seeing this as a total psycho move that will get Mao kicked in the face by BRitain.
[5] I'll address the UK eventually, but with a former British colony falling to Communism almost immediately after independence, Churchill looks a lot better in the 1950 elections and he narrowly wins (instead of narrowly losing). 
