During the past 65 years of military rule in Burma, the army has killed thousands of people from almost every one of the country's numerous minorities: Shans, Karens, Kachins, Karennis, Mon, Chin and many smaller groups. But the only ones who have faced a genocide are the Rohingya, and it is happening right now.
Only two-thirds of Burma's 52 million people are ethnic Burmese, and almost all the other groups have rebelled from time to time because they have no autonomy. Indeed, the original military takeover in 1962 occurred to stop an elected civilian leader from creating a federal state where the minorities would have some control over their own affairs. But the 1.1 million Rohingya are special, because they are almost all Muslim.
The other minorities are all Buddhist, at least in theory, and the army only kills enough of them to quell their revolts. The Rohingya never revolted, but Muslims are feared and reviled by the Burmese majority. Now the army claims that the Rohingya are all recent immigrants from Bangladesh, and is trying to drive them out of the country.