As unsound as it is to reduce a complex phenomena into a single person, the reason for the ascendancy of Waterloo over Leipzig is Napoleon. The French Emperor was not just a supreme warlord, but a symbol for an age of dramatic changes; when Goethe met Napoleon in 1808, the German poet saw Napoleon as one of the signature personas of his era. Whether loved or hated, Napoleon managed to exert a degree of cultural force that lasted throughout both the nineteenth and twentieth centuries. The popular European memory of Napoleon was never static, but it was something that was kept alive in various media. The longevity and transnational nature of "Napoleon" was something his predecessors and contemporaries possessed.

Within this context, it was perhaps inevitable that Waterloo became the natural end point for the military career of Napoleon. Even though the Hundred Days were a long-shot gamble, the idea that Napoleon was on the verge of victory was a narrative that was common in British memory and reified by popular historians like Creasy. Napoleon's military star fell with Waterloo. The same could not be said of Leipzig. Although the Battle of Nations did destroy French hegemony over the continent, Napoleon still remained master of France. The central geostrategic question of 1813/14 was whether or not the Bonaparte dynasty would continue to rule France and what the shape of France's frontiers would take. That Napoleon lost both of his dynastic rights and France the "natural" frontiers and Low Countries was a testament to the hole Napoleon had dug himself into after Leipzig. Nonetheless, there was a brief window of opportunity for Napoleon to cut a deal with the Allies in late 1813. The resulting 1814 campaign was fodder for Napoleonic legends of recovery and betrayal, but it had none of the drama of either Leipzig or the later Waterloo. Thus the aftermath of Leipzig did not have the same sense of finality as Waterloo.

Waterloo also benefited from its proximity to Britain and the emerging industrial era. Waterloo was a pioneer in the phenomena of battlefield tourism and new technologies allowed it to be a short excursion for the upper-classes of the late Georgian period. Relics, real or phonies, also became part of Britain's tourist culture as panoramas and museums celebrated and recreated the battle. Additionally, Waterloo cemented Wellington's position in the hierarchy of British politics, so the battle's memory had a powerful patron. Waterloo veterans received special medals and other rewards, which rankled some of Wellington's Peninsular veterans who were not in the Low Countries but had seen far more campaigning than the relative tyros of Waterloo. All of these various memory projects helped elevate Waterloo into a global event, especially as British culture dispersed through the globe over the long nineteenth century.

Leipzig was a shadow of this type of commemorative practices. Tourism and commemorations were present, but not on the scale of Waterloo in Britain. Nor did Leipzig's Coalition generals achieve the same level of political success as Wellington. Schwarzenberg, Blücher, and von Bennigsen received honors and rewards from their monarchs, but the state structures of Austria, Prussia, and Russia did not have much room for military men in the running of government. Even Charles John, the newly-elected Crown-Prince of Sweden and former French Marshal, enfolded his actions in 1813 as part of a larger restoration of Swedish power that he inaugurated. Moreover, as befits its title as the Battle of Nations, Leipzig had many victors. In comparison, Waterloo had two- Wellington and Blücher- and Anglophone commemorations gradually erased the latter from the battle.

However, Leipzig did have great importance in Central European memory of the Napoleonic Wars. While Prussian, and later German commemoration of the Napoleonic period held that Waterloo (or Belle-Alliance in German) was the terminus of Germany's victory over the French, but Belle-Alliance was the capstone to the arch of Germany's Befreiungskrieg. Leipzig was an important element of this commemoration. The Befreiungshalle in Kelheim exemplified this Central European process of commemoration. The interior of the neoclassical building has a bronze shield bearing the major battles of the Befreiungskrieg, including both Waterloo and Leipzig. German-language novels of the Napoleonic period and other forms of media did not differentiate between the 1813 campaign and its aftermath in 1815 as two unrelated campaigns, but rather treated them as a discrete whole. German Romanticism as well as the nationalist movement lionized the spirit of the German volunteers against France, and their regimental colors of black-red-gold became the symbolic colors for the 1848 revolutions. Although the Hohenzollerns were opposed to the Paulskirche parliament and its tricolor, it did lay claim to the martial spirit of the volunteers and this state-sponsored memory culture became more salient after German unification.

The centennial celebrations of Leipzig were quite large in Germany, especially as the Kaiserreich unveiled the Volkerschlachtdenkmal a Wilhelmine structure lack the refinement of Kelheim's temple. But the Teutonic grace of the Leipzig monument was a suitable metaphor to the somewhat churlish turn German memory of the Napoleonic Wars took after unification. While Blücher had maintained that such a battle could bear two names, the Wilhelmine era witnessed an increasing resentment that Britain had stolen Prussia's, and by extension, Germany's, hard-won glory in 1815. Leipzig thus represented less of a multinational victory by the twentieth century, but instead became a German victory.

This close association of Leipzig to a larger pattern of German militarism had dire implications after the World Wars. While Waterloo could be connected to Britain's attempts to save the continent from a hegemonic tyranny, Leipzig was more problematic, especially after Germany's defeats in 1918 and 1945. Celebrating Leipzig tapped into a wider pattern of German militarism and traditions that allegedly led to figures like Wilhelm II and Hitler. On a more practical level, Allied bombing also inadvertently destroyed the Prussian War Ministry's archives, which also made it much harder for historians after 1945 to revisit the 1813 campaign. The Cold War also served to diminish the importance of both 1813 and Leipzig for the West. It was difficult for Western researchers and reenactors to visit Leipzig since it was part of the GDR or consult the surviving archives. Ironically, the 1813 campaign received a brief renaissance of sorts within the Warsaw Pact as the Soviets presented Russian liberation of Central Europe from the French yoke as a precursor to the Red Army's victory over fascism. This politicized take on 1813 further discouraged Western military historians and writers to explore 1813 and Leipzig.

The net result of this is that while Waterloo's is fading in European public memory, it still commands a degree of weight that Leipzig lacks. Even though Abba's "Waterloo" gets all of the history wrong, it still shows the extent to which this battle retains a degree of narrative force. Popular military history is not above these cultural trends. The term "decisive" is one that professional military historians tend to avoid, but it is a word that caters to popular tastes. The close association of the battle with Napoleon's political fortunes imparts an inherent drama and a clear end to the battle that is not present in Leipzig. Finally, Waterloo is a much more plastic memory than Leipzig. Waterloo can mean many things, whether a symbol of a triumphant British resistance to the continent or as a metaphor for giving into love. Despite its arguably greater importance to Napoleon's fate, it is much harder to make Leipzig culturally relevant.

I don't have as many sources available, but what I can tell you is Waterloo was more decisive in a metaphorical and public view stance than Leipzig due to a myriad of factors.

Primarily it's because of the after effects. The loss at Leipzig was of course a serious blow to French power, but it also was only significant in Germany as it dissolved the Confederation of the Rhine. What it failed to do where Waterloo did was demoralize the military establishment of France.

As Napoleon made his way north to Paris he often confronted officers dispatched to arrest him and convinced them to rejoin his ranks. This was because the Officers and even more so the average Infantrymen had a very firm confidence in their Emperor's command and strategic resolve. They still felt as if there was a gamble to be made at Waterloo.

One can say the effects of the First French Empire losing it's sway over Eastern Europe, Spain and Germany as a progressive and looming cataclysm. With each defeat Napoleon lost the confidence and support of more and more soldiers and officers until the effects were on his own army, arguably the most reliable from the start.

To put it bluntly Napoleon did not mind if he lost the confidence of his wavering German allies. But he truly knew the game was up when his own armies Officers and Soldiers told him it. At Waterloo the support and resolve of his most seasoned support structures faltered and inevitably so did his resistance to the Congress of Vienna.