Hindsight bias is a view achieved after the event, in review of the circumstances. This perspective creates a biased view based on afterthought, rather than a balanced view based on the information available at the time. An idea, action or opinion may seem great or idiotic in retrospect, but the hindsight factor obscures the basis of the thinking. There's also a tendency to think that things were more predictable than they actually were.
Examples of Hindsight Bias:
These are common examples of general historical hindsight bias which don't include the obvious lack of knowledge prevailing in their times:Napoleon's invasion of Russia was never a feasible military option.
World War Two was preventable.
The Vietnam War was a mistake.