1950s was the era when the Mongols chased the Vikings away(ngrams.googlelabs.com)
ngrams.googlelabs.com
1950s was the era when the Mongols chased the Vikings away
http://ngrams.googlelabs.com/graph?content=vikings%2Cmongols&year_start=1850&year_end=2000&corpus=0&smoothing=3
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