Is it because of their declaration of war with France when it was (for argument's sake) unnecessary? Or was it because they simply needed to scapegoat them to curb their economic development?
Why did no one blame Austria for their aggression towards Serbia?
follow up: are future historians likely to link the two world wars together, like, say, we link the Roman Punic wars together as one continuous conflict with brief respites of peace?
More of course can be said, but the FAQ does have a few answers which might be relevant for you!