My Dialectic Seasonal-Decade Theory

Winter late 1900s early 1910s
Spring late 1910s early 1920s
Summer late 1920s early 1930s
Autumn late 1930s early 1940s
Winter late 1940s early 1950s
Spring late 1950s early 1960s
Summer late 1960s early 1970s
Autumn late 1970s early 1980s
Winter late 1980s early 1990s
Spring late 1990s early 2000s
Summer late 2000s early 2010s.
Note that crises occur in late summer.