One aspect of historical reporting of the war is the overwhelming impression that there was a near universal enthusiasm for the whole project at the start. Not in the prelude to the war. Everyone accepts there was widespread opposition, mainly from the left across Europe, but that it crumbled away after the war broke out. There's a large element of truth in that, a lot of people rallying to their various flags across Europe when push came to shove.
But it ignores the obstacles to peaceful opposition which were put in place across the world.
First and foremost large numbers of young men were being sent away to fight. Parents, relatives, friends and neighbours would turn out to bid them farewell and wish them the best. In such an atmosphere it might not be easy to express anti-war sentiment.
Most European countries had some system of national service in place, so there was a precedent to being called up and sent away. Where that was not the case and conscription was introduced it provoked much more conflict and open debate, but that was later in the war.
Everywhere there was censorship, to differing degrees and enforced differently. Censorship nonetheless, of both opinion and news. Newspapers and magazines could be censored or shut down, printing presses seized or destroyed. Meetings and demonstrations could be banned or broken up, activists beaten up or arrested. Expressions of pro-war sentiment would often be tolerated or encouraged, the police standing by when there were anti-German riots in the UK, for example, or when there were anti-German and anti-Jewish pogroms in Russia.
Another near-universal was the banning of strikes. A strike during wartime became equated with treason, so even when its aims were purely material it acquired an anti-war aspect, intended or otherwise.
Similarly with demonstrations. They may or may not always have been banned - there were big anti-conscription demos in London later in the war, for instance - but they were always in danger from attacks from pro-war mobs or the police.
At the start of WW1 many thought that it would all be over by Christmas, or some such optimistic hope, and far too many were swept away on a tide of patriotism. That wouldn't last.