The Napoleonic Wars were a series of conflicts involving Napoleon's French Empire and changing sets of European allies by opposing coalitions that ran from 1803 to 1815. As a continuation of the wars sparked by the French Revolution of 1789, they revolutionized European armies and played out on an unprecedented scale, mainly due to the application of modern mass conscription. French power rose quickly, conquering most of Europe, but collapsed rapidly after France's disastrous invasion of Russia in 1812. Napoleon's empire ultimately suffered complete military defeat resulting in the restoration of the Bourbon monarchy in France. The wars resulted in the dissolution of the Holy Roman Empire and sowed the seeds of nascent nationalism in Germany and Italy that would lead to the two nations' consolidation later in the century. Meanwhile, the Spanish Empire began to unravel as French occupation of Spain weakened Spain's hold over its colonies, providing an opening for nationalist revolutions in Spanish America. As a direct result of the Napoleonic Wars, the British Empire became the foremost world power for the next century, thus beginning Pax Britannica.