Why did Napoleon and reign make European leaders eager to restore the monarchies?

Napoleon's conquests spread the ideals of the French Revolution, such as nationalism and liberalism, which threatened the traditional monarchies across Europe. His rise to power demonstrated how revolutionary fervor could upend established governments, leading many European leaders to fear the instability and chaos that could arise from popular uprisings. In response, they sought to restore monarchies as a means of re-establishing order and stability, and to counteract the spread of revolutionary ideas. The Congress of Vienna in 1814-1815 aimed to reinforce the balance of power and restore conservative regimes to prevent a repeat of the Napoleonic upheaval.