Just an opinion, but all the historians seem to share it.
In their books they justify their opinions with hard evidence from a hundred years of research.

Here is Margaret Macmillan, a Canadian historian,

"Most of the poets who were widely read at the time – notably Rupert Brooke – were writing patriotic verse, and the "futility of war" line only emerged later. "Britain certainly thought it had legitimate reasons for going in, and I think it did," she says. "
http://www.theguardian.com/books/2014/jul/25/margaret-macmillan-just-dont-ask-me-who-started-war

"Soldiers did not fight just because they were afraid of their officers. The toughest discipline was in the Italian army, which had the highest rate of desertion among the Allies. Soldiers fought for something. Indian soldiers, as their letters reveal, for honour, the British for king and country. As one French soldier said simply, 'I do not want to become a Boche.' "

"Stevenson argues persuasively that we must believe that men and women meant what they said when they talked about duty and sacrifice, that they accepted the war, even willingly."
http://www.lrb.co.uk/v26/n23/margaret-macmillan/von-hotzendorffs-desire

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