Since you have posted the same piece, I will post the same extract.

"the real 'recruiting boom' began in the last week of August, when news of the British retreat following the Battle of Mons reached Britain. Recruiting peaked in the first week of September.[2]
By the end of September, over 750,000 men had enlisted; by January 1915, a million."

"The timing of the recruiting boom in the wake of the news from Mons, though, suggests that men joined knowing that the war was dangerous and indeed many joined precisely because it seemed to be a threat to their home, district and country."