The best example of cause and effect after the Congress of Vienna is Napoleon was defeated, so France started a revolution. Austria won territory in Italy, so Italy adopted Austrian customs. Spain became a monarchy, so the French empire was weakened. the French empire was demolished, so liberal ideology grew.

Spain became a monarchy, so the French Empire was weakened

Explanation:

Congress of Vienna was conducted between 1814 - 1815, in which the participants are Britain, Austria, Prussia, Russia, and France who were super powers at the time.

The purpose of Congress of Vienna was to achieve peace in Europe after the French Revolutionary Wars and the Napoleonic Wars, such that each of the powerful European super powers can have or shared same powers that balance each other's out.

Hence, the Congress of Vienna led to the establishment of the Spanish monarchy which sought to balance the power in the Europe and to limit Napoleon's movement, this in turn, results to the French empire to lose its recent conquests.

Hence, the right answer is that, Spain became a monarchy, so the French Empire was weakened

fighting to keep abortions legal