Task: Question Generation
Input (English): Passage: The 6000-mark war  was a war between Denmark and Sweden which took place from 1276 to 1278. It started because of a disagreement over an agreed sum of 6,000 silver marks for Danish assistance to Magnus Birgersson in the battle against Valdemar Birgersson in 1275.
Output (English): How many years passed from the battle against Valdemar Birgersson to the beginning of the 6000-mark war?