Somehow, I see an agiographic reading of WW1, and the need to find a sense of destiny that was completely lacking.
The war started in a very casual way, and certainly no politician (much less general) was anticipating a long, debilitating war in 1915.
Internal interests, bloody-mindedness and in general an absolute lack of foresight was dominant all over Europe.
- A-H was worried by the autonomist feelings among the Slavs, and saw a "short, victorious war" as the best way of ensuring that the empire would be strengthened and unified again. The Serbian successes in the Balkan wars were threatening the Austrian position in the Balkans, and increasing Russian influence in the region.
- the German Heer was eager to go to war at the earliest possible opportunity, before Russia might sort out its political trouble, and benefit from the economic boom under way
- the french were obsessed by revanchism: any chance of paying back the Huns was a good one.
- the Asquith government was focussed on the Irish problem, and was not anticipating a war. All the FO papers indicate that the balkan situation is considered normal, and no threat of major war was anticipated. The odd guy was Churchill, with his anti-german obsession. It is well known that in June 1914 he decided - on his own authority alone - to have the Mediterranean fleet joining the Home Fleet for exercises in the North sea. This obviously angered the Germans, but also Asquith was not amused. Churchill might have been replaced there and then, if only the government had been stronger. The other Churchillian contribution was the decision to seize the two turkish dreadnoughts built in UK: not exactly the best way to keep Turkey friendly.
- the Russian situation was more messy than usual: I already pointed out the economic boom. Unfortunately, the political situation was not improving, and the early concession of a Duma was mostly a symbolic act. The weakness of the Czar, the plots of the German czarine, Rasputin, the contrasting interests and ambitions of the grand dukes, the growing unrest : all the ingredients for a disaster were there.
The British Government declared war without a great enthusiasm. However, the first months were not so bad: the western front held (a repetition of 1870 was certainly one of the possible scenarios, and the russians were quite enterprising and successful in Prussia. Gallipoli is born here: Churchill - who fancied himself a great strategist - devised a plan that might end the war soon (and would also ensure that the fleet - and the First Lord of the admiralty - would be seen as the winners): the landing at Gallipoli, forcing the straits, and hopefully knocking out Turkey from the war (a repetition of the first Balkan war). The Russian reverses in early 1915 just strengthened the commitment to the Gallipoli option: now opening a route to send supplies to russia (and to export Russian wheat which would have paid for those supplies) was even more necessary.
Once the Gallipoli gambit has failed, and the russian situation is worse due to more austrian troops available in galicia, the political situation is even worse in St. Petersburg: Nicholas is no Alexander, much less a Stalin. The closer german troops are to his capital, the more his depression will increase, the more insistent will become the czarine and Rasputin (was he really on the German payroll? maybe, maybe not). In this scenario, the Champagne offensive is more than necessary, and cannot be delayed.
It is easy, 90 years later, to say "use wisely your resources, don't waste them: it is only a matter of time, the Entente will prevail". I doubt that such a wise advice might have been given in 1915, or acted upon by the British or the French (and, please, no Usa-ex-machina: in 1915 - and in 1916 - the USA is firmly neutral, and Wilson will campaign on a neutrality platform in 1916. The USA have never been involved in alliances, and it would be quite difficult to anticipate their entry in the war).