I'll post part of an answer I gave earlier; these are essentially the turning point(s) of the First World War.

1. The Somme, Verdun & the Brusilov Offensive in 1916; 2) American Entry into WWI in 1917; and 3) Operation Michael & the Second Battle of the Marne in 1918

1. Verdun and the Somme ate through German manpower reserves, and destroyed what remained of the professional, pre-war core of the Army. Starting with the instalment of the Hindenburg/Ludendorff Junta (or, 'Hindendorff' [tm] as I call them) in September, 1916, 1.3 million men were combed out of industry, convalescent wards, the 1917 conscription class, the old, and the internal military structure. However, in order to backstop their plans for the army, emphasizing more materiel over men, they instituted the Hindenburg Programme for armaments, which saw the exact same amount of men sent back to the Reich to work in farming and industry. The Reich could only shift around forces, lacking reserves. Meanwhile, the Brusilov Offensive had gutted the Austro-Hungarian war effort, requiring more German involvement in the East, in turn stretching German resources almost to the limit. This tightening of the noose lead directly to Unrestricted Submarine Warfare in 1917, which lead directly to:

2. American entry into the war; with this, American government-to-government loans could backstop the Allied war effort well into the future. This, combined with American industry and manpower, drove Hindenburg and Ludendorff to seek an end to the Eastern Front, achieved by Lenin's coup, thus allowing 500 000 troops to be sent west. Unfortunately, the punitive treaty of Brest-Litovsk meant that 1.5 million men stayed in the East.

This brings us to #3: 1918. The Germans launched the Michael Offensive, achieving success largely due to numbers; the BEF was undergoing a manpower crisis, while the sheer number of guns and divisions opposite them virtually guaranteed a breakthrough. Losses among the vaunted 'stosstruppen' units spearheading the offensive were horrendous, over 40 000 casualties on the first day, and c. 350 000 in the following 6 weeks. The offensive had no strategic or operational goals whatsoever, was utterly lacking in combined arms cooperation, and was a complete failure: British forces held on, French troops aided them (and Foch became supreme commander), and counterstrokes were being made, before American manpower even made it's presence felt. The last gasp was the so-called Friedenstum or 'Peace Offensive' at Soissons, which failed spectacularly and was swiftly followed by the Second Battle of the Marne, and ultimately, the great Allied victory at Amiens on August 8th, 1918, which spelt the death knell of the Kaiserreich, and of German hopes for dominance of Europe, and Weltmacht (World Power).

Essentially, although German/Central Powers chances of success had been greatly reduced by 1918, it was the beginning of the Hundred Days Offensives that really signalled the end for the Germans. After that, defeat was really only a matter of time.

You could make a very strong case that there wasn't anything approaching an "inevitable outcome" of the war until the failure of Operation Michael. March 21st, 1918 as the opening salvo of what was planned to be their last-dithed breakthrough moment to roll up the entire French line, the Ludendorf launched an "artillery bombardment beg[inning] at 4.40am [...] The bombardment [hit] targets over an area of 150 square miles, the biggest barrage of the entire war. Over 1,100,000 shells were fired in five hours.." (http://www.historyofwar.org/articles/battles_sommeII.html)

Following this massive - even by WWI standards - barrage, the special reserves of stormtroopers - specially trained in advanced combat tactics such as fire and movement tactics, so effective that they remain a core element of virtually all fireteam maneuvers even today - were able to utilize the fortuitous cover of fog to penetrate deep into British lines virtually undetected. The results were devastating: by the end of the 1st day of Michael, more than 20,000 British soldiers had been killed and another 35,000 taken out of action, while the Germans had managed to penetrate the Fifth Army's line in several areas, causing the entire British Army to be in full retreat by the second day.

Unfortunately for Germany's military, its Supreme Commander Ludendorf's overall "strategy" was... well... a lack of coherent strategy. When questioned as to his decision-making by the Crowned Prince of Bavaria, he replied, "the army chops holes, and then we'll see what follows." This lack of vision and reliance on a que seras, seras mentality would prove to be the undoing of all the gains Germany would make in this operation.

In spite of the initial successes, the British army was able to regroup and fortify (in large part due to Ludendorf's initial failure to recognize and follow up on their collapse). German military might would be expended attacking British positions, time and again. The turning point would come on March 28th, when the ill-conceived Operation Mars would at last be repulsed entirely by the British line.

Around this time, the Allies had (finally) realized that their system of independent military commands was horribly hobbling their overall war aims, and had agreed to quasi-unify them under the central authority of Ferdinand Foch.

Over the course of the following days, German advances began to falter all across the line - due in large part to terrible supply shortages and difficulty moving what supplies they had through to the front fast enough to reach the starving, low on ammunition front lines, as well as and a failure of artillery to reach the advancing front in time to be of use to the Germans.

The impetus and goal of Michael was to force the French and British the the peace table on German terms before the newly-allied USA could get enough of its own troops across the Atlantic to make a difference. But as train-full by train-full of the new reinforcements stiffened the Allied backbone, the already-flagging German advance was halted altogether at the critical city of Amiens a key strategic point for Allies and Germans alike in this operation.

By April 5th, Ludendorf had called off the remainder of Operation Michael entirely. From the standards of WWI battles, it might have been thought of as an unqualified success - hundreds of miles of new territory that had been allied was now occupied by the German Army. Yet for all that, it had failed to break Allied resistance, and now left the German Empire facing tens of thousands of fresh American troops arriving daily to supplement the already numerically-superior French and British forces. What's more, having exhausted their supply of crack stormtrooper units in the now-futile attempt to break through once and for all, Ludendorf's army was now left with the under-fed, under-trained, un-equipped dregs - a force that would never again be able to mount such an effective attack as Michael.

He would try - four more times, and each less effective than the last - but Ludendorf's failure in March 1918 effectively ended German hopes for victory after four years of fighting. This isn't to say that it meant total defeat for Germany, though. Up until the humiliating and ultimately catastrophic terms of the Treaty of Versailles were presented, many in both Germany and among the Allies themselves expected it to be a negotiated peace that would end the war: after all, they would remain on French and Belgian territory right up untilt he end of the fighting... they'd never lost Germany and, in the eyes of a fair few, the German military had never been defeated, only betrayed by their own defeatist elements within the population - a sentiment that would fester for a further 2 decades before rearing its head once more. Still, whatever hopes the Kaiserreich might have held for such a peace to be reached on German terms ended with the strategic failure of Michael to break the Allies' back.

I'm not sure I understand the question. Are you asking if the end of the war was inevitable before the surrender?

Germany lacked the industrial capacity and population to successfully win a drawn out war. Some say the war was lost after the first Battle of the Marne. Others argue that Germany could have come out with a negotiated peace, had it adopted a different strategy on the western front.