What it says on the tin. There's been plenty of discussion about getting the US into the Central Powers/aligned with Germany, but few about an Anglo-German rapprochement in the years prior to WW1. Thus, the challenge is that with a POD after January 1st, 1900, get Britain to be a part of a *Central Powers, or at the very least, once the *Great War kicks off, have them aligned to Germany, Austria, and the Ottomans, facing off against France and Russia.