Gas attack: is just another type of weapon used to win a terrible war faster and there is a reason why its banned.(I think its banned if it isn't shame on us)
British empire did a lot of terrible stuff in its life but so did a lot of other nations.
British blockade compared to Germany blockage: both terrible maybe not equally though.
concentration camps: by reading some of the information posted on this topic and other I know. I must say most or all major nations around the World wars time had some sorted of concentration camps.
Austria-Hungarian empire starting world war 1: ok yes they did declare war on Serbia which result Russia declaring war on them, then Germany declaring war on Russia, and so on.
Civilian
****, and killing: War can change a men into animals which results in this non soldier behavior,(Its sad really for the victims) But a few incidents is all it needs to paint a picture of a army even if that's just a few bad apples and not all of them.
WAR IS WAR and that's sad because a nation, a group, or even a alliance could do anything to turn the odds in their favor even if it'll cost lives, breaking laws, using banned weapons, pleasing the soldiers or starving a city or nation. Everyone has blood on their hands in wars sad to say.