Final answer:
The correct answer is d) The Concert of Europe.
Step-by-step explanation:
The Congress of Vienna, which took place from 1814-1815, was a peace conference that aimed to rebuild European relations after the Napoleonic Wars. One of the main outcomes of the Congress was the establishment of the Concert of Europe, a system of diplomacy and alliances among the major European powers.
This system helped maintain political stability in Europe for nearly forty years, preventing major wars from breaking out. However, this period of stability came at a cost, as conservative governments ignored liberal and nationalist movements, leading to future revolutions.