Black Swans are large impact, hard to predict rare events beyond the realm of normal expectations based on experiential knowledge. Truly, there have only been two black swan event of that proportion in the past 26 years - and that was the stock market crash in 1987 and (at least for us Americans isolated by two oceans) was the collapse of World Trade Center in September 2001.

Evolving Systemic Risks in Credit Markets
However, there have been some disruptive systemic risks to the global financial system since 1987, beginning with the Asian Contagion of 1997, as well as the Russian default and LTCM debacle in 1998. Systemic risks to the global financial system like we had in 1987 and the close calls we had in 1997 and 1998 scares border on being unquantifiable and unknowable events fraught with "Knightian Uncertainty."