Played a few run on veteran and expert difficulty:
Solo German on veteran (AH and Ottoman Played by AI): France First, easy victory over Belgium and almost reached Paris before the first Winter, than the lines started to freeze, and it took me over a year to take the final two hex towards Paris (while clearing the french fortress system), managed to clear most of the UK fleet, and sneak past the UK ships a few landing craft, after that, managed to clear both France and UK in early '16, could take out Russia faster probably, but wanted the Victory March in London.
Expert Central Powers: Tried twice, failed twice. First Russia first, struggled with Serbia and while destroyed the Russian troops, could not take enough territory, and after Italy joined and France DOW-ed on Netherlands it was over. The naval war was brutal, but with careful management of the fleet you can take some victories and keep the ships alive, but you will not get a decisive victory by this ever, and the other side can repair any damage, so only kills matter. The main issue on the land, that when the opponent gets lvl 1 art, they will just destroy 1 unit in every 5 turn (lvl 1 shell around the same time) and when they get lvl 2 art, they will destroy 2-3 unit in every 2-3 turn, or 1 unit per turn, just with art, and you simply cannot keep up with that. Second run tried the France first, did a better job in Serbia, and pushed them to nish, but could not clear the balkan, belgium was done quite fast, and managed to wipe three UK troops with an encirclement early, but then stopped, and even forced to fall back to the original borders, keeping only the fort from belgium, got unlucky and failed to take Verdun by only one damage, but even with that it was a losing position from there. keeping Italy out of the War is almost a must, only with a quick balkan can you hope to face the Italians, and even with that, it will mean you lose the AH fleet. The ottomans in this almost managed to take Egypt, but ultimately failed Next time probably will try Serbia and Russia first again, with better prepare for the French DOW and avoid Italy, if possibly, Romania can be knocked out quickly, with a well timed preventive strike.
Entente: Played only on veteran, but with the Triple Alliance, so Italy also in the CP, making it at least Expert the difficulty, but differently, not as much bonus but lots of units. First time it was a failure, italy broke through and from there the Germans also started to take territory, and France surrendered before the US entered. Second time it Went better, Managed to hold Italy, and give up territory for the Germans only slowly, still, lost Paris in late '15, while trying to do damage with the Russians, since their numbers at the early game allows you some encircling and elimination, even with the horrendous combat penalties. Serbia held out until '16 at the original border, but after Montenegro fall to the Italians, Serbia also had to abandon Belgrad. Greece and the UK strike the Bulgarians, and took Sofia quickly, and later with the Romanians managed to force the Bulgarian surrender. From there Gallipoli also taken and a few units managed to slip into Ottoman teritory on Asian side. Victory at Bagdhad and partial victory at Mecca also took toll on the Ottoman Moral, but ultimately the US won the war, despite the horrendous naval defeat they suffered from the Italians.
On how to win with CP on Expert: Hold the Line on the west, invest heavily into entrenching, and hope it will help, as well as infantry weapon, since that helps a bit against artillery. Take any opportunity to punish the french (and focus on them, if possibly, they have smaller income than the UK and France together.) try to keep every fort (the belgian on after the DOW) and take any if opportunity presents, but never overextend for it. Save the Belgian units from certain destruction, you can transport them from the ports to germany to keep them alive, extra units always welcome, just keep in mind, you cannot rebuild them, but can repair them. Be prepared for the same with netherlands, only the units outside the country will remain, so evacuate them, transports also an option if cut of. the fort also a grate prize, but might fall on DOW turn, so it may be tricky. end the extra troops to serbia, to force than out fast, and gain Bulgaria fast too, also helps Romania staying out, but sooner or later you need to take that out anyway, so you might just do it now. Than decide on italy, if you fold with AH, you can save yourself from an extra enemy with 10+ ships, 30+ land units and around 200 mpp per turn income, but lose 10K-15K AH morale (you might able to pay this with the balkan victory) and 100-150 mpp per turn for a while, as AH devastated. Also the AH units will be useless for 3-6 turn. No good choice, so it is a great choice and decision. Irrelevant from this, you want the Russians out ASAP, so they are the next target, push them with the Balkan units, that are no free, and hope a quick victory, time is on the entente side. if Russia out before '17, you are maybe good, if not, you are in trouble, as the Entente starts to get Bigger in economy and tech and morale and you will fall into the negative spiral of defeat.