Is germany really the cause of WWI?

After WWI ends, the treaty of Versailles really takes a toll on Germany and punishes them for building up their army even though they were not the first country to mobilize its army. How is Germany responsible for the cause of the war when they didnt make the first move? Or are they responsible because they built up there army for the reason of taking over neighboring countries. This would be just like if the United States was being punished by Great Britain because they have to many missles and their navy is to big. What gives the right for Germany to be punished after the factwhen they were only trying to build up their own military preparing for the oncoming war?