In simple terms, the Congress of Vienna was convened to clear up the appalling mess left behind by several decades of conflict in Europe. For over three decades the continent had been wracked by bloody, bitter conflict, which could ultimately be traced to the French Revolution and its seismic political impact.
After the fall of the Directory in 1799 and the subsequent rise to power of Napoleon, Europe was plunged into even greater chaos as the Corsican general embarked upon a radical program of territorial expansion, destroying long-standing political arrangements such as the Holy Roman Empire, which had lasted for over a thousand years before Napoleon forcibly dissolved it in 1806.
The French Revolution and the rule of Napoleon had severely undermined the old social and political order on which pre-revolutionary Europe had been based. What the crowned heads of Europe regarded as dangerous ideas such as liberalism and nationalism had captured the imagination of millions. But with Napoleon now defeated and safely in exile on the island of Elba—or so everyone thought—the political elite of Europe hoped to turn the tide of history back towards monarchism and conservatism.
Hence the Congress of Vienna, which attempted to establish a long-term peace plan for the shattered continent. Even the most die-hard reactionary understood that there was no prospect of turning the clock back to how things used to be before the fall of the Bastille. Instead, the only realistic option available to the delegates at Vienna was to effect a balance of power in Europe that would prevent a single nation from becoming too powerful and from dominating all the others as Revolutionary and Napoleonic France had done.
This involved the comprehensive revision of existing national boundaries, with France inevitably the main loser as vast swathes of the territory she had acquired over the past three decades were divided up among the victorious Coalition powers.