The Battle of Killiecrankie was fought between Highland clans supporting James II and "English" troops (though mostly lowland Scots) supporting William of Orange on July 27th, 1689 during the Glorious Revolution. Although it was a stunning victory for the Scots, it had little overall effect on the outcome of the war, and their forces were scattered at the Battle of Dunkeld the next month.
After William of Orange deposed James II, the Scots were divided on what to do. The Stuart line had sat at the head of the combined Scottish/English throne for some 300 years, and had not caused them problems. Furthermore his throne was lost primarily because he was a Catholic, as were many Scots. A convention was called in Edinburgh and it was decided to accept William and Mary, both Protestants, as their King and Queen to maintain the joint throne. In addition it was declared that the Church of Scotland was officially Presbyterian, and unlike the church in England, the Scottish throne had no direct control over it.
A number of people, notably highlanders, decided this was insult enough, in particular John Graham of Claverhouse, Viscount Dundee. When summoned to the convention, he refused to attend, and instead he left for the highlands in order to raise an army. Calling themselves Jacobites, latin for James, they planned to restore James to the throne of Scotland.
Sir Ewen Cameron of Lochiel, Chief of Clan Cameron, set about forming a confederation of highland clans loyal to James as soon as William had arrived in England. When Dundee raised the Royal standard for James at Lochaber, Ewen estimated he was likely to receive about 1,800 men and a few cavalry.
They soon learned that a governmental force of about 3,500, led by General Mackay of Scourie, had been raised in the lowlands and was marching for Inverness. Dundee was determined to intercept Mackay near Blair Atholl, astride the road through the hills that Mackay would have to pass. Many of the clans had not arrived yet, but he set out anyway and ordered them to follow "with all haste." Ewen himself also had a force of about 240 Camerons with him at the time, and tried to catch up while he dispatched his sons to raise support along the path of march. Ewen overtook Dundee just before he reached Athole, where they were joined by about 300 Irish, under the command of Major-General Cannon.
Dundee held a quick war council with those clan leaders that had arrived, and then immediately set out for the field with his force, now numbering about 2,400. He arrived at the pass before Mackay and set up position on a ridge above the pass. When Mackay arrived they saw they had no hope of attacking Dundee's force, they they instead deployed in a line and started firing on them with muskets.
The Scottish line was shorter than the English, due to the disparity in numbers, leaving Ewen in the middle with an open flank on the left. By the time all of the forces were formed up it was late afternoon and the Scots had the sun in their eyes, so they simply waited for sunset under the dulsitory fire from Mackay's forces.
At seven o'clock Dundee gave the order to advance, at which point the entirety of the Highlanders dropped their gear, fired what few muskets they had, and charged. Mackay's forces, realizing the battle was on, stepped up their rate of fire. Eventually the lines met and Mackay's men in the center were "swept away by the furious onset of the Camerons." The battle soon ended with the entirety of Mackay's force fleeing the field, quickly turning into a rout that killed 2,000, Mackay included.
However the cost of victory was enormous. About one-third of the highlander force was killed, along with Dundee himself near the end of the battle. The latter loss would prove fatal to the Jacobite cause.