Which 1815 congress redrew the map of Europe after Napoleon's defeat?

The Congress of Vienna, which took nine months, was chaired in effect by Metternich, and famously did not meet. There was no plenary session of the whole congress; the business was done by the four great powers in private, with the smaller states waiting, and the endless balls and receptions served as the venue where the actual negotiating happened.

The settlement was aimed at balance rather than justice. Territory was traded to make sure no single state could dominate again, France was given lenient terms so it would not become a permanent grievance, and the map was drawn with no reference to what the populations wanted - which stored up the nationalist explosions of 1830, 1848 and 1870.

It nonetheless worked better than anything before it. There was no general European war for 99 years, which is the longest such stretch in the modern record, and the Concert of Europe it created is the ancestor of the League of Nations and the Security Council. Talleyrand, representing the defeated power, talked his way from suppliant to participant so effectively that France ended up joining the inner group deciding the terms.