The Karen National Union, the official name of the Karen rebel army, has been fighting Myanmar's (Burma's) military and government since gaining independence from the British 60 years ago. But their rift largely started before that, during WWII when the Karen sided with the British, and the ethnic Burmans with the Japanese.
Japan invaded Myanmar in 1941, and fighting between Japan and the Allied forces continued through 1945, wrecking havoc on local land and populations. During negotiations for Independence from Britain, the Karen lobbied for autonomy from Burma, and for their own land. The Karen National Union (KNU) was created in 1947, and Burmese independence was gained from Britain in 1948, though the Karen requests went unacknowledged.
As Burma, and later Myanmar, the country has had a consistent track record of repressing ethnic minorities, including the Karen.
Shortly after independence from Britain, attempts at negotiations between ethnic groups who called for an end to such treatment and the government were met by military oppression. The Karen rebel group and other ethnic resistance armies began sprouting up in response.
KNU was one of the largest, claiming at one point to have an army of 14,000 fighters, and controlled large swaths of territory along the eastern border, according to the BBC. In more recent years, as Karen rebel groups have splintered, the number of their fighters has decreased and the group has lost control of strategic land.
The KNU’s political agenda is no longer relevant to all Karen communities, according to the Transnational Institute.