Complex sentence: With Christianisation in 1000 came the tradition of fasting and a ban on horse meat consumption, but the event which probably had the greatest impact on farming, and hence, food, was the onset of the Little Ice Age in the 14th century.
Split into simpler sentences: With Christianisation in 1000 came the tradition of fasting and a ban on horse meat consumption. More significantly in terms of farming and food supply was the onset of the Little Ice Age in the 14th century.