Did Germany lose World War II when/because "kill ratios" started moving "against" her?

All answers to this thread mostly modulate the fact that kill ratios drive the war. They are correct: there are indeed more factors that simple kill ratios, for two good reasons:

• Kill ratios are determined by other factors: tactics, technology, moral....
• A kill ratio is bearable or not for a country depending on its resources

Still, it is interesting to follow how kill ratios evolved alongside those factors. On the land, Germans maintained most of the time a kill ratio in their favor and still lost ground and units that they did not intend to loose.

On the sea however, the situation was entirely different: the U-BootWaffe campaign against Allied shipping on the Atlantic and the Indian Ocean was a total defeat as soon as 1943, and in this specific strategic context, the kill ratio is an indicator to follow: In 1943, the Germans lost the battle of the Atlantic because sinking one Allied ship was too expensive in numbers of submarine lost.

Eventually, even on the sea, kill ratio is not the only factor: the other important indicator of victory for the Allies was that they started to pass convoys with no losses: this meant that the Germans had no more ways to fight against Allied reinforcement in United Kingdom: this allowed the Allies to enter a new phase of the war: the Normandy landings.

In a battle or campaign, there are several stages; the attack, the killing, and the exploitation of the advantages gained by the battle and resulting killing.

In the invasion of Poland, for example, the Germans began by inflicting physical casualties at the rate of two or three to one on four Polish armies (out of seven), defending the northeastern, northwestern, southwestern, and southern parts of the country. This led to Polish prisoner captures of 10 times or more the German physical casualties in the exploitation sequences following the initial breakthroughs, and the destruction of the Polish armies. The end result was that the four German columns could "gang up" on the single Polish army defending Warsaw (the other two were in the Soviet zone).

In the invasion of France, the penetration of the Allied lines via a thrust through the Ardennes resulted in the splitting of the Allied forces, north and south. The Germans then destroyed the northern force (except for the survivors of Dunkirk), then overwhelmed the now outnumbered and outgunned southern force.

In Russia, the ratio of physical casualties was something like two Soviets for one German, but German armored thrusts exploited the resulting breakthroughs and the captures of large "bags" of Soviet prisoners at Smolensk, Kiev, and elsewhere, that caused the disproportionate Soviet losses of both manpower and land. In 1942, the ratio of physical casualties remained at about 2 to 1 for most of the year, but the Soviets had "wised" up and lost far fewer prisoners. And point of the defense of Stalingrad (before the November counterattack), was that city fighting would prevent an exploitation sequence such as a German thrust down the Volga to Astrakhan, and the reinforcement of the southern Caucasus thrust. By late fall, the onset of winter and the weakening of German armored forces allowed the Soviets to counterattack, and enjoy their own exploitation sequence by surrounding Stalingrad.

Although the Germans initially inflicted physical casualties of five to one, on the Americans at Kasserine Pass during the early going, a heavy artillery bombardment and German supply shortages prevented any exploitation sequence, so the early favorable results (for the Germans) became meaningless.

Bottom line, kill ratios can be important, but only to the extent that they set up the exploitation sequences like the ones discussed above. Absent such exploitation sequences, their importance is limited.

As mentioned by many here, kill ratios are only really significant if you're talking attrition warfare or at a basic tactical level. Otherwise they're an effect of losing the war, not a cause.

The underlying question of why those kill ratios turned against Germany is a very complicated one, but one important aspect is that the Germans had invented a new kind of mobile warfare and the Allies had to play catch up.

People often fail to appreciate just how much tactics and technology changed from 1939 to 1945. In the air, all-metal, monoplane military aircraft had only just replaced the biplane in front-line service (and in some cases, such as the Fairey Swordfish, it hadn't). On the ground, radios were bulky and expensive, and communication was still a laborious process often done by runners or cable. Tactically, many units and vehicles still lacked radios limiting the sophistication of their maneuvers and tactics; you can only get so fancy with flags and flares. At sea, the aircraft carrier was still untried, and the submarine still unconquered.

The Germans exploited this technological change by increasing the pace of warfare dramatically. They introduced radios at the tactical level, in individual tanks and aircraft. They trained their air, infantry, artillery, and armor to work in concert. They imbued local commanders with the know-how and ability to adapt to the local situation and make local decisions without waiting for orders form higher command. They added paratroopers to overcome strategic obstacles, and tactical air strikes to support deep penetrations.

The situation was now liable to change in hours rather than days. This is a pace the Allies were not prepared for. It's a pace that allowed the German army to find gaps and exploit them before the Allies could react. At this pace, the Allies could never be quite sure of where the Germans were. Superior Allied forces were surrounded and cut off as they raced to defend positions that had already been overrun. Faced with this chaotic situation, the Allies often retreated if they were unsure of their flanks.

The Germans ran rampant with this new style of warfare from 1939 to 1941, but the remaining undefeated Allies were learning. The Soviets and British learned through facing the Germans, being defeated, and having to rebuild their armies. The Americans were also building an army, but they had the luxury of doing it in peacetime, observing what was going on in Europe, and learning from it. The North African campaign let the US Army learn some hard lessons at a relatively small cost through defeats like Kasserine.

Kill ratios are a tactical consideration - the Allies were more interested in beating Germany from a strategic position: deprive it of resources and manufacturing capability, and overwhelm it with mass production and superior logistics. It's fortunate that Monty, Patton and Zhukov were excellent tacticians, but it was Eisenhower and Shaposhnikov, with the support of civilian political leadership, who truly understood how to beat the Germans with logistical supremacy in support of an aggressive offense.

This was also U.S. Grant's strategy during the end phase of the Civil War, and the kill ratios strongly favored the South (nota bene: Cold Harbor).

The only time "kill ratios" really matter all that much is when using attrition warfare.

While important in World War I, to the best of my knowledge, this strategy was never employed in a large scale on the fronts Germany was involved in.* The Germans themselves went out of their way to avoid this kind of warfare, instead preferring fast exploitation of front breakthroughs to cut the communications (and force the surrender) of large numbers of enemy units.

The Germans' basic problem was that they had less resources (in both men and material) than their opponents, so in the long run any serious losses on their side, regardless of ratios, would doom them. Russia could have afforded to operate at a deficit in losses the entire war, and still could have won, as long as they could make it up more than the Germans could.

Eventually the Germans stretched themselves too thin on the Russian front, and the Russians were able to gather enough forces to start achieving their own breakthroughs. If you keep track of "ratios", perhaps things started to swing in the UN's favor at this point, but the underlying issue was that the German forces couldn't replace their losses on anywhere near the scale that the Russians could. Any changes in loss ratios you may see at that point are a symptom, not the cause.

Have any historical accounts attributed Germany's early successes to the their massive early "kill ratios," and their subsequent lack of success to the fact that their "kill ratios" fell below their overall numerical disadvantage?

Professional historians would never attribute something as complex as the development and unfolding of the Second World War in Europe to 'kill ratios'. That's history in a vacuum since you're leaving out all other aspects of the war and concentrating on pure ratios and math, thus leaving out context. 'Kill ratios' are in effect a reflection and form part of the result(s) of what historians study, research, and write about, they are not the main theme or area of concentration.