King James IV was obliged to invade England in order to honor the Auld Alliance with France, because France had been attacked by Henry VIII of England who was in cahoots with the Pope.
King James IV was brought to battle by the Earl of Surrey, Earl Marshal of England, and totally routed. King James IV, nine earls, thirteen barons and thousands of others were killed in Scotland's most disastrous battle. King James IV had never wanted war against Henry VIII and had done everything in his power to prevent it. The Auld Alliance, which was extremely useful to France on occasion, was a disastrous union from the Scots point of view.
The following Clans fought at Flodden for the King: Buchanan, Campbell, Fraser, Gordon, MacFarlane, MacKenzie, MacLaren, MacNaughten, Sinclair, Skene and MacLean.