Why was the Congress of Vienna considered a success?

The Congress of Vienna was consider a success because of three main outcomes.
One Britain gained control over several strategic colonies and become the first superpower of the world. Two Russia extended its powers and received souveranity over Poland and Finland. And three Europe brought peace between the nations for almost 40 years.

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http://www.sparknotes.com/history/european/napoleonic/section10.rhtml

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