Little Ice Age
A centuries-long cold spell (c. 1300-1850) whose crop failures helped topple governments from Ming China to Europe.
For roughly five centuries, the planet ran cold. From about 1300 to 1850, average temperatures across parts of the Northern Hemisphere fell by around a degree Celsius, and in the worst stretch, the 1600s, winters bit harder than anything Europeans had known for a thousand years. The River Thames froze solid enough to host 'frost fairs,' full carnivals of tents, ox roasts, and printing presses set up on the ice. Alpine glaciers ground forward and swallowed villages. In Greenland, the Norse colonies that had farmed since Viking times simply died out. This was the Little Ice Age, and its lesson is not that cold kills, but that cold destabilizes.
What made it cold
No single switch turned the temperature down. Historians and climate scientists point to a stack of causes acting at once. The Sun grew quiet: the Maunder Minimum (roughly 1645 to 1715) saw sunspots nearly vanish, trimming the solar energy reaching Earth. Volcanoes did the rest, hurling sulfate haze into the stratosphere that dimmed sunlight for years. Iceland's Laki eruption in 1783 and Indonesia's Tambora in 1815 each helped produce a 'year without a summer.' Shifts in ocean circulation, and possibly the regrowth of forests over land emptied by plague and conquest, may have deepened and prolonged the chill. The point is that the climate system has many levers, and several were pulled cold together.
The general crisis
Here is where a geopolitics reader should pay attention. The historian Geoffrey Parker, in his 2013 book Global Crisis, argues that the coldest decades of the 1600s coincided with the most violent wave of upheaval before the twentieth century. Harvests failed, food prices spiked, and hungry populations turned on their rulers. Parker counts revolts, civil wars, and state collapses on nearly every continent within the same few decades: the Thirty Years War that killed up to a third of central Europe, the English Civil War, the Fronde in France, revolts across the Spanish empire, and, most dramatically, the fall of China's Ming dynasty in 1644 amid famine and rebellion. He does not claim the cold caused these wars. He argues it was the extra shove that pushed already-strained societies over the edge.
Threat multiplier, not trigger
That distinction is the whole value of the case. A society with full granaries, competent government, and slack in its food supply can ride out a run of bad harvests. A society already stretched by war, taxes, and inequality cannot, and failed harvests become the spark in a room full of gas. The Little Ice Age did not decide history; it loaded the dice. Some states adapted and some fell, and the difference lay in their resilience, not their thermometers.
That is exactly the language modern planners use when they call climate change a 'threat multiplier' for conflict in the Sahel or the Middle East. When defense departments war-game drought and crop failure driving migration and unrest, they are running Parker's argument forward three centuries. The Thames no longer freezes over, but the logic that turned a cold century into a violent one has not gone anywhere.