1916, The Late Entries.
''Revanchism had, for the moment, died in the trenches of Elsass and the streets of Paris.''
-Alexander Lucas, historian, 1973.
With Russia bowing out of the War, and suffering increased disorder as the country remained uncertain just how radical the Revolution was, Yuan Shikai, President of the Republic of China [1], realised that China, despite the internal instability it was facing [2], was in a position to enter the war at little risk. While French Indochina was still a threat, they had been cut of from France and the Entente for more then a year, and the French forces there were in no position to go on an offensive.
With this in mind, China declared war on France on the 21st of April, and moved to occupy the French (and Russian, but on the motivation of ‘restoring order’, not being at war with them) concession in Hankou.
On the other side of the world, the Plan that, it was hoped, would end the War was about to go in effect.
On the 9th of May, a co-ordinated offensive by German, Dutch and Belgian forces, supported by Austro-Hungarian expeditionary forces, and strengthened by the arrival of reinforcements from the East begun, moving for Paris via Bastogne, which was still under French occupation.
By the 19th of May, the Allies were pushing out of Belgium, and into France, and by the 7th of June, one day before Yuan Shikai died [3], Paris was reached.
It took a week of fighting to take the city, and the French government had moved to Bordeaux towards the beginning of the war, but it was, nonetheless, a blow to French morale, as was the fall of Tananarive to German-Dutch forces on the 16th of June, and the fall of Hanoi to German-Dutch forces (aided by being able to land in southern China and then march south) on the 17th of June.
As France took what little forces guarded the Spanish frontier to throw against the Allies, in an attempt to stop the advance, Spain’s government, though painfully aware of the Kingdom’s military weakness, saw a chance, and took it.
On the 30th of June, Spain entered the Great War as a member of the Allies, convinced by France's weakness and Germany's promises of colonial gains.
[1] He didn’t declare himself emperor in TTL.
[2] Compared to OTL, China is far more calm, given that the National Protection War never occurred, and isn't occuring (see above).
[3] That is, two days after OTL.