Which identifies the effects of the congress of vienna?
the unification of germany led to the seven years’ war.
the harsh treatment of france led to a rise in nationalism throughout europe.
an interconnected europe led to the creation of the european union.
the congress system it set up became a model for the united nations.

The correct answer is "The congress system it set up became a model for the United Nations".

The Congress of Vienna was held between late 1814 and during 1815 and gathered ambassadors from all European states. The idea was to negotiate a viable manner of keeping a long lasting peace in the continent, specially after the French Revolutionary Wars and the Napoleonic works. Most of the participants were conservative politicians who intended to defend the status quo from the emergence of nationalistic and liberal revolutionary movements. It has actually beendescribed as a reactionary alliance in favour of returning the power to the hands of the absolut monarchies. This congress set the international political scenario until the outbreak of World War One.

It was actually the first time in history, in which representatives from the different states sat together and discussed agreements and treaties. Previously, they only had sent messages to each other, but they had never gathered. This is why it is said that Congress of Viena set the model for current international politics, and for the functioning of supranational organisms such as the United Nations.

The congress system if set up became a model for the United Nations.

Explanation:

My authority source for choosing answer C is the United Nations itself.  UN Chronicle, the magazine of the United Nations, featured an article titled, "From the Congress of Vienna to Present-Day International Organizations" (December, 2014).  That article asserts points such as these:

the hereditary right of a monarch to rule from the mandate of heaven

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