The best example of cause and effect after the congress of vienna is

1) napoleon was defeated, so france started a revolution.

2)austria won territory in italy, so italy adopted austrian customs.

3)spain became a monarchy, so the french empire was weakened.

4)the french empire was demolished, so liberal ideology grew.

The answer is: 3)Spain became a monarchy, so the French empire was weakened.

The establishment of the Spanish monarchy was initiated to balance the power in the Europe and to limit Napoleon's movement. After the congress, several empires united against the advance made by the French  Empire.  Not long after the congress of Vienna, French empire started to lose its recent conquests.