Held in 1814-1815, after the Napoleonic wars, the Congress of Vienna was a gathering aimed at the goal of reorganizing Europe, and stomping out any ideas the people had against them after the events of the Napoleonic wars. However, some of the aspects of the congress ended up contributing to a war in the future, specifically WWI..
Alliances: With the alliance among the major European powers, looking to collectively prevent Napoleonic actions, it ended up creating risk of backfire. Like the principal of intervention, which allowed them to intervene with what they thought was right, opening up opportunity to accidentally dig into bonds with other nations, causing tensions leading to WWI.
Imperialism: With the Congress of Vienna aiming to redraw the map of Europe, shifting power and territory around. Some of the changes made with the redrawing didn't acknowledge the wants and needs of the populations, and were never resolved, leading to the tension in the people for WWI.
Conservatism: Because the Congress was made of mostly conservative monarchies and aristocracies, their primary goal was to regain the status quo that napoleon messed up. And while aiming to regain stability, those who wanted individual rights started revolting.
.
Liberalism: With the congress rebuilding conservative monarchies and acting near oblivious to the populations wants and needs, it sparked liberal movements and encouraged those in the movements to continue growing the fight against the status quo, the clashes between the two fueling future fights,