The Karen people's relationship with Burmese independence was fraught from the start. As Britain prepared to hand over power, Karen groups resisted incorporation into a Bamar-dominated state but could not agree among themselves on the boundaries of their proposed homeland or how far to press their demands. On 17 July 1947, the Karen National Union headquarters ordered the creation of Karen defence militias -- the Karen National Defence Organisations. When the dominant Anti-Fascist People's Freedom League offered the KNU a Karen state within Burma that October, the KNU refused, insisting on more territory. It was the kind of impasse that independence movements create and rarely resolve: two peoples sharing the same geography, each with legitimate claims, neither willing to concede enough ground to prevent a war.

Following Burma's independence, intercommunal violence flared in the Irrawaddy Delta. The government blamed the KNDO, though other Karen militias were likely responsible. Prime Minister U Nu and Karen leader Saw Ba U Gyi toured the delta together, trying to build trust between communities edging toward conflict. In a remarkable gesture, U Nu allowed the KNDO to recapture the town of Twante from the Communist Party of Burma -- but Bamar news organizations, poorly informed about the operation, reported it as a Karen insurrection, and panic spread through Yangon. On 1 September 1948, joint KNDO and ethnic Karen military police seized Thaton and Mawlamyine in an uncoordinated first move that alarmed the central government. Five days later, the KNDO voluntarily returned Mawlamyine, but the damage was done. Trust had been replaced by fear on both sides. Then came Christmas Eve: a Bamar militia attacked a church service in Palaw, killing 200 Karen worshippers. After that, the slide toward open war became unstoppable.

On 31 January 1949, the KNU formally declared war. Four days later, the KNDO was outlawed. U Nu organized Sitwundan militias to confront the Karen fighters, and these forces surrounded the KNU headquarters in Insein, where local KNDO members had already raided the armoury. Reinforcements were called in, swelling the garrison to over 400 fighters. The KNDO even infiltrated Mingaladon airport, just four miles from Insein, though they chose to capture only ammunition rather than attempt to hold the airfield. While Insein became the focal point, the KNDO's reach extended far beyond it. Karen forces controlled much of the countryside, including Hinthada District in northern Ayeyarwady Region, and had captured cities stretching from Mandalay and Pyin Oo Lwin in the north to Mawlamyine in the southeast. The Burmese government teetered on the edge of total defeat.

After 111 days, the KNDO retreated from Insein into the countryside, their goal of capturing Rangoon unfulfilled. The consequences rippled outward for decades. The Burmese Army's commander-in-chief, Smith Dun -- himself an ethnic Karen -- resigned in the aftermath, a casualty of the impossible position the conflict created for Karen officers serving in the national military. The army's near-collapse emboldened hardline militarists who began demanding that General Ne Win seize power. He obliged in 1962, beginning a military dictatorship that lasted in various forms for half a century. The Karen conflict itself never ended. What started at Insein in 1949 became one of the world's longest-running civil wars, with Karen armed groups continuing to fight for autonomy in the borderlands of eastern Myanmar. The Irrawaddy newspaper titled one retrospective simply: "The Battle of Insein Never Really Ended." For the Karen people, that remains literally true.