Complex sentence: In the United Kingdom, white Christmases were more common from the 1550s to the 1850s, during the Little Ice Age, but during the 20th century there were only seven official white Christmases in the United Kingdom.
Split into simpler sentences: In the United Kingdom, white Christmases were more common from the 1550s to the 1850s, during the Little Ice Age. During the 20th century there were only seven official white Christmases in the United Kingdom.