Between 1300 and 1850, the Earth experienced a Little Ice Age whose cause to this day is not known.
A blog post at Interesting Engineering has more details including the consequences and some paintings from the period. The causes listed are interesting:
The causes of the LIA are still not known, while potential candidates are reduced solar output, changes in atmospheric circulation, and volcanism.
Low sunspot activity is associated with lower solar output, and two periods of unusually low sunspot activity occurred during the Little Ice Age: the Spörer Minimum (1450–1540) and the Maunder Minimum (1645–1715), which is named for astronomer E.W. Maunder who discovered the absence of sunspots during that period. Both of these coincide with the coldest years of the LIA in parts of Europe.
Another possible candidate is a reversal of the North Atlantic Oscillation (NAO). This is a large-scale atmospheric-circulation pattern over the North Atlantic and adjacent areas. During its “positive” phase, the track of North Atlantic storms is centered over the British Isles and Northern Europe. During its “negative” phase, cold Arctic air from Russia moves over northern Europe.
A final candidate is volcanic eruptions which propel gases and ash into the stratosphere, where they reflect incoming sunlight. In 1783, Iceland’s Laki volcano erupted, and in 1815, the Tambora volcano on Sumbawa Island erupted.
I am voting for low sunspot activity. Your thoughts?