Their intended practical purpose was to protect shoes and socks from mud or rain, but they also served as a feature of stylish dress in accordance with the fashions of the period.

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Increased informality may have been the primary reason for the decline in the wearing of spats.

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A revival of high-top shoes with cloth uppers was forecast to replace them.

~ https://en.m.wikipedia.org/wiki/Spats_(footwear)