Hi, I made an extremely comprehensive post about the major battles of the war in broad strokes and this includes Verdun and the Somme along with analysis of the state of Germany's war effort. The relevant bit is:

What is most important though is that the Somme ripped the initiative from the Germans. They gained it in February that year but the Somme would put them on the perpetual defensive for the remainder of 1916 and 1917, only to be temporarily reinvigorated in 1918 for a last ditch all in offensive which would fail shortly (we'll speak on that later). The Somme terrified the German high command. They could not suffer another Somme under the current conditions without capitulating. They would thus begin construction of a massive defensive fortification called the Siegfriedstellung, the Hindenburg Line. It was a massive defensive 'line in the sand' with, literally, barbed wire fields hundreds of meters deep and support trenches and tunnels and concrete pillboxes and so forth. It was a force to be reckoned with. In early 1917 the Germans would withdrawal to this line called Operation Alberich. This would cede even more territory to the Anglo-French forces.

Some historians point toward the Somme and Verdun with retrospect as the battles which lost Germany the war because we can look at them with a fine lens. We know that the battle caused the retreat of Germany to the Siegfriedstellung and we know from writings of various officers that they admit the German army could not sustain another battle like that without cracking. While in Spring/Early Summer 1916 Germany looked like it was going to obliterate the French army it would now be permanently placed on the defensive acting, mostly, in a reactionary fashion toward Entente offensives. They would spend the entirety of 1917 on the defensive and perform one last offensive in Spring 1918 which was in many ways born out of desperation and a last stand of sorts.

TL;DR?:

The dual battles of the Somme and Verdun bled the Germans dry and stole the initiative from them. It put them permanently on the defensive and, combined with the incredibly effective blockade, basically spelled doom for the German war effort. As I explained in the first part of this post the German war effort was completely neutered by self destructive economic policies and said blockade by 1918. However it was the American contribution which pushed the war over the edge. With 10,000 soldiers landing per day in France Germany was about to have millions of completely fresh troops facing up against their troops which had been fighting and dying for four years. They had a last shot after breaking Russia's back in throwing the weight of their Eastern forces along with elite battalions of their best men (again, something I go into depth in the aforementioned link) and basically went for an all or nothing offensive to seize Paris and push the British back into the sea. With primarily American and French help this offensive would be stopped in its tracks and with the combined three armies and now millions of men the Entente would have no trouble at all rolling over the Germans.

Okay that wasn't short at all. TL;TL;DR:

The war was, in a retrospective sense, a lost cause for Germany after the Somme and Verdun in my opinion. However there was no reason for them to surrender after the battles as they did still have a lot of fighting men and weren't in complete shambles yet; we just have the benefit of hindsight and knowing how things developed. It was the injection of American men that really tipped the balances in 1918 which forced Germany to perform a desperate offensive, allowed the Entente to repel that offensive, and operated majorly in the 100 Days Offensive.

Way too long bro what's the easy to digest one sentence quip so that I can show off too my friends?

Germany, in all likelihood, would have been lost with or without American intervention post 1916 but America gave the Entente the extra push to end it much quicker and that can not be understated in a war that was claiming as many lives as it was per month.