In 1919, the Treaty of Versailles was signed, which included a “War Guilt” clause, where Germany was forced to claim they were guilty for the First World War. From a purely historical context, was Imperial Germany truly the one at fault for the First World War? If so, why? And if not, then who?

This is the most repeated historical intentional/unintentional mistranslation.

The "war guilt" clause article 231 is truncated in it's meaning. It was a necessary preamble to payment of reparations for the damages caused in France and Belgium, where Germany must accept that it was the cause of that destruction in order to justify paying for it. This never made much debate among the allies, and it wasn't intended to be a "guilty for the whole war happening" clause in the first place.

However it was presented immediately as such in Germany at the time, and history did the rest.

Germany's allies had to sign similar articles, which simply posed the legal basis for reparation payments.