Jack of Harts

The Shang bombarded New Washington during The War, leveling the capital city and driving ash into the air.  That alone would have caused a period of global cooling that might have lasted a year or two.  But the bombardment caused tremors that stretched out for scores of kilometers in every direction, resulting in the eruption of numerous nearby dormant volcanoes.  The ash they spewed into the air started a global Ice Age that continues to this day.