The history of the world's religions is a history of military conquest, which is to say, a history of slaughter, and Buddhism is no different. It was spread by Ashoka the Great who conquered the Indian state of Kalinga. Buddhist apologists say Ashoka grew disgusted with war after the horrors done in his name and then became a Buddhist—but they wave away the fact that he kept Kalinga in his empire.
Buddhist scriptures include stories of violence. For example, in the Nirvana Sutra, the Buddha tells of killing Hindus in a past life:
When I heard the Brahmins slandering the vaipulya sutras, I put them to death on the spot. Good men, as a result of that action, I never thereafter fell into hell. O good man! When we accept and defend the Mahayana sutras, we possess innumerable virtues.Some Buddhists rationalize that as an example of "compassionate killing"—they say the Brahmins were killed so they would not bear the sin of continuing to slander Buddhism. That's a fine example of the logic of all religious terrorists.
Buddhism has a long tradition of warrior monks. In Japan, they were Sōhei. In Tibet in 1959, the defenders of Tibet's feudal system were primarily monks—their tradition of violence includes the assassination of King Lang Darma in 841 for failing to support the Buddhist monasteries. That killing is still celebrated:
It's described at Tibetan Monks Tour: Cultural Events as "Feeling great compassion toward the King, who was going to suffer immensely as a consequence of the sins he was committing against his people, Lhalung Pal Dorji shot an arrow at the heart of Lang Darma. The king was dead on the spot. Peace and harmony was restored in Tibet." To be more precise, the power of monasteries was restored. The great majority of the people continued to be serfs. (For more on the Lang Darma, see Was Lang Darma a Buddhist?)
Wikipedia, a good place to start (and a bad place to stop) researching, has more on Violence in Buddhism.
The most recent examples of Buddhist terrorism are in Sri Lanka and Myanmar:
Enforced disappearances in Sri Lanka: "A 1999 study by the United Nations found that Sri Lanka had the second highest number of disappearances in the world and that 12,000 Sri Lankans had disappeared after being detained by the Sri Lankan security forces."
Sri Lanka Buddhist monks destroy Muslim shrine.
Sri Lanka Muslims decry radical Buddhist mosque attack: "Video of monks and other hardliners trying to storm it later showed one monk addressing the crowd in overtly racial terms, saying the campaign against the Muslim building was a victory for "those who love the race, have Sinhalese blood and are Buddhists"."
Buddhist monks incite Muslim killings in Myanmar: "An examination of the riots, based on interviews with more than 30 witnesses, reveals the dawn massacre of 25 Muslims in Meikhtila was led by Buddhist monks - often held up as icons of democracy in Myanmar. The killings took place in plain view of police, with no intervention by the local or central government. Graffiti scrawled on one wall called for a "Muslim extermination." "
Burmese Buddhist monk Wirathu uses YouTube to spread anti-Muslim hatred to thousands.
ETA: BBC News - Why are Buddhist monks attacking Muslims?:
One of the most famous kings in Sri Lankan history is Dutugamanu, whose unification of the island in the 2nd Century BC is related in an important chronicle, the Mahavamsa. It says that he placed a Buddhist relic in his spear and took 500 monks with him along to war against a non-Buddhist king. He destroyed his opponents. After the bloodshed, some enlightened ones consoled him: "The slain were like animals; you will make the Buddha's faith shine."