I know that after Napoleon was decisively crushed at Waterloo, the victorious powers used the Congress of Vienna to attempt to redraw Europe to create a "Balance of Power" where no power would be too strong to defeat each other.
However, after listening to Dan Carlin's "Blueprint for Armageddon" podcast, I noted that he did say that the unification of Italy and Germany impacted the balance of power, which ultimately led to the First World War.
Historians: to what extent did these unifications impact Europe? How did they change the balance of power? If any of you had an answer to these questions, it would be much appreciated.
Thank you!
The German and Italian unifications, although taking place in the same cultural moment (more or less) were very different from each other and happened under very different circumstances.
Italian unification was a complex series of events encompassing both social upheavals and military confrontations. The Kingdom of Sardinia-Piedmont, an improbable polity in existence since the War of Spanish Succession in the early 18th century, was originally ideated as a buffer state between France and the Austrian empire, the post-Napoleonic hegemon in Italy.
The Italian Unification process was a thorn in the side of both the Austrians, who saw themselves challenged on the Italian Peninsula, as well as the French, who had initially backed the process only to get cold feet when the new Kingdom of Italy made clear its intention to end the Papacy's temporal power (early on, Piedmontese politicians has more or less agreed their goals were only the unification of Northern Italy, leaving options open for the continued existence of the Papal States in some form or other).
So the presence of a polity challenging Austrian Hegemony in Italy itself altered the balance of power; the Piedmontese rulers intervened in the Austro-Prussian war in order to occupy the Austrian-held parts of Italy. If you want to ultimately stretch this new geo-political situation to the start of the First World War, by the time tensions in Europe were coming to a head in 1914, there was a large and united Italy while parts of the Austro-Hungarian Empire continued to be inhabited by ethnic Italians (Trentino, Istria, and Dalmatia). The pretext for war was evident.
You can read all about post-Napolenic italy in: Davis, John A. Italy in the Nineteenth Century, 1796-1900. Oxford: Oxford UP, 2000. Print.
The unification of Germany was a threat to both French but particularly the British empire. One was that after the Franco-Pressuian war and the Paris peace of 1871 the new Germany took hold of the Alsace-Lorraine region, giving a huge boost to German industry and also a severe blow to the French industry.
Secondly a railroad from Germany through Austria-Hungary and to Turkey would severely damage Britain's borderline monopoly on trade from the Far East. Instead of sending ships all around Africa and London you would then be able to just send them up through the Persian gulf and load everything on trains there. Sure it might take a month, but the travel time would be shortened. It would also reduce Britain as one of the main distributors of goods from the Far East since now everything would go through Germany.
A third reason was that a unified Germany now allowed them to properly build up their naval power. Britain has always been reliant on being the number one naval power to not only maintain control of the colonies and trade, but also because they're an island. If they don't control the seas then they risk being isolated and will be at the mercy of whoever controls the seas. If Germany controls the seas then they can pretty much say "Give us India or we'll block all your ports". So in short it makes Britain a lot more vulnerable and their position as the world number 1 much more uncertain.