The French Ambassador asked Britain to join France and was told no. He was astonished and told the British Cabinet that the Foreign Secretary had promised British support, and as a consequence, France had moved all its Atlantic fleet to the Med for action against the Austro-Hungarian Empire, leaving France's Atlantic ports open to German naval attack.
This was the first time the Cabinet had heard of the Foreign Secretary's promises.
So, as a matter of honor, the British Cabinet voted to declare war the following morning.
With tragic results.
National World War I Museum and Memorial
There has been quite a bit more written in the past 2 decades due to more original source material having become available with many of those authors presenting detailed talks and discussions...all in one place. Many different playlists, audio/visual etc.
What more virtual museums and history sites should emulate.