as you say just the Zimmerman telegram would not be enough. The Germans did need a better propaganda department.
To make a big change you would need no credit to either side and some ting like cash and carry policy and this would have made the Entente run out of resources much faster.
As for the grandiose dream of an empire that put the Germans in the same boat as all the other powers in Europe with the massive empires.
The real difference of no American troops arriving in Europe would be the Entente lacking the manpower to break the German lines and the German may not have wasted the manpower on the last offensive in 1918 to break allied lines and kept those troops for defence.
Hence my quote about being "selective" with the truth highlighting the Germany aggression while omitting your own (until the Bolsheviks opened the secret diplomatic files.) Even after the secret diplo files were released, the citizens of war were in it to win it, full of spite, and the British still had control of world-wide communications via the telegraph lines it had cut at the start of the war.
As for many power, let's go on a deep dive:
The AEF had 4 divisions (20 k men, + 10k division tail) for 120,000k by the end of 1917 (some still training/organizing), the small tail was partially due to American eagerness to fight, partially due to American arrogance about Elan and Infantry marksmanship vs entrenched arty and machine guns that everyone had already learned (even Cadorna!) by 1917. To their credit they did learn eventually but Perishing did a fine job killing them. By 1918 11 months IOTL the division tail got a bit better at 1:1 with combat at 2.6-2.8 million with 64 divisions.
In contrast the Liberal Prime Minister Lloyd George withheld 400,000 men from conservative favorite general Hauge in early 1918 all the while it was state policy to make it a white man's war by withholding deployment and expansion of the 2 million strong Indian army. Insert snip about British perfidy of asking others to die while it withheld its own men. You'd never know it by looking at British pictures and dispatches that 1/3 of the western front manpower was Indian in the panicked days of 1914-1915 but this was dialed back so white men can die (and preserve the empire); this self-imposed restrain can be reversed if they felt they were desperate. The same with the Dominions, which had just started conscripting in mid to late 1917 and vast pools of farmboys to throw. There was so much slack in the British empire, unused for various reasons that they can mobilize.
This is in contrast to the Germans who had mobilized all the men from 18-45 hoping to fight a short war, then realized that they over mobilized and along with amazing mismanagement of the food-supply and domestic politics (turns out beating and shooting people really inspires revolutionaries) had to steadily demobilize their most experienced older men, the subversive (pacifist/liberal/any one that made a big fuss) men, and the farmers in exchange for fresh conscripts all while taking causalities everywhere. The East proved to be a manpower drain with most of the food going to feed the local garrisons sent to loot the food, it turns out revolutionary chaos, 3 years of scorched earth retreats, Tsar Nick's malicious mismanagement, and some poor weather had all reduced the harvest. By 1918 there was only about a million men in reserve, which the Spanish flu hit hard since the Germans had the same frontage, but less men to spare.
Rubber, trucks and oil were not so important to the Germans in ww1 as they are mostly using trains and horse-drawn transport. rubber, trucks and oil were much more important in ww2 to the Germans and this explains why they used so many horses in ww2 when the British had stopped using them.
Steel tires (which the Germans used in desperation) churned up the road and made logistics worse for follow-up elements. A horse/mule eats as much as 7-8 men (can't just forage grass), requires a handler to maintain, and is taken away from food production which the central powers lacked in contrast to the more mechanized British/French farmers who also had world markets. The 100 days offensives were combined arms breakthroughs spearheaded with hundreds of tanks and sustained by trucks and early APCs. In contrast the Spring offensive sent new echelons of men to sustain breakthroughs but can only walk so fast and came at the cost of slaughtering the best and most reliable men of the German army (and couldn't exploit due to the severe shortage in horses). You simply couldn't carry enough on foot and horse in a speedy manner that the defender couldn't ship in via rail.
At the end of the day, there's no getting around the fact that Moltke and Conrad von Holtzendorff pushed for a quick glorious war against over half the world's economy and manpower and reality handed them a war of attrition.
The unrestricted submarine warfare may not have happened if the UK had not included food are part of the blockade of Germany.
Traditional food was not included in naval blockades.
So? He did it first America sempai, so you should understand when the Kriegsmarine kills American citizens? Also please ignore all the true war crimes the British are publishing about us too.
America clearly didn't care, the state department took a decidedly pro-British stance in 1914 when Americans on Central Powers and Entente ships alike were being killed and decided to only protest the German sinkings. Once the block aid set in there were obviously a lot more Americans dying on Entente ships than the Central Powers.
